Topics to be Learn

  • Introduction
  • Histology
  • Epithelial Tissue
  • Connective Tissue
  • Muscular Tissue
  • Nervous tissue
Tissue, Organs, and Organ-Systems
  • Tissue: A group of cells with the same embryonic origin, structure, and function. Example: Muscle tissue.
  • Organs: Large functional units made up of various tissues that work together in an organized way. Example: Kidneys.
  • Organ-System: A combination of organs working together to perform a specific function. Example: Respiratory system.
Cells in the Human Body

Number of Cells: Human body contains about 100 trillion cells of 200 different types.

Types of Cells:

  • Somatic Cells: All body cells except sperm and ova. Example: Skin cells, muscle cells. 
  • Germ Cells: Cells related to the reproductive system. Example: Sperm and ova.

Histology

Histology: The study of the structure and arrangement of tissues. Focuses on the microscopic organization of tissues.

Types of Animal Tissues:

  1. Epithelial Tissue: Covers body surfaces and lines organs.
  2. Connective Tissue: Supports, connects, or separates different types of tissues and organs.
  3. Muscular Tissue: Responsible for movement.
  4. Nervous Tissue: Transmits signals in the body.

Know This!

  • Marie Francois Xavier Bichat (1771-1802): French anatomist and pathologist. Discovered tissue. Known as the ‘Father of Histology.’

Epithelial Tissue (epi: above, thelium: layer of cells)

Characteristics of Epithelial Tissue

Structure:

  • Cells are tightly packed with minimal intercellular matrix.
  • Supported by a non-cellular basement membrane.
  • Cells can be polygonal, cuboidal, or columnar in shape.
  • Each cell has a single nucleus located centrally or at the base.
  • Tissue is avascular (lacks blood vessels) but has a good regeneration capacity.

Function:

  • Primary function: Protection.
  • Other functions include filtration, secretion, absorption, and transportation.

Types of Epithelial Tissues

1. Simple Epithelium:

  • Made up of a single layer of cells.
  • Subtypes: a) Squamous Epithelium, b) Cuboidal Epithelium, c) Columnar Epithelium, d) Ciliated Epithelium, e) Glandular Epithelium, f) Sensory Epithelial Tissue, g) Germinal Epithelial Tissue

2. Compound Epithelium:

  • Composed of several layers of cells.
  • Subtypes: a) Stratified Epithelium, b) Transitional Epithelium

Basement Membrane

  • A non-cellular membrane on which the lowermost layer of the epithelium rests.
  • Acts as a scaffolding for epithelial growth and regeneration after injuries.

Simple Epithelium

(i) Squamous Epithelial Tissue

  • Location: Blood vessels, alveoli, coelom, etc.
  • Structure: Composed of a single layer of polygonal, thin, and flat cells. Cells have serrated margins and a centrally placed spherical or oval nucleus. Appears like flat tiles from above, also known as pavement epithelium.
  • Functions: Protection, absorption, transport, filtration, secretion.

(ii) Cuboidal Epithelium

  • Location: Lining of pancreatic ducts, salivary ducts, proximal and distal convoluted tubules of nephron.
  • Structure: Cuboidal-shaped cells with a centrally placed spherical nucleus.
  • Functions: Absorption, secretion.

(iii) Columnar Epithelium

  • Location: Inner lining of the intestine, gall bladder, gastric glands, intestinal glands.
  • Structure: Tall, pillar-like cells with narrow inner ends and broad, flat free ends. Oval or elliptical nucleus located in the lower half of the cell. Free surface has numerous microvilli.
  • Functions: Secretion, absorption.

(iv) Ciliated Epithelium

  • Location: Inner lining of the buccal cavity of frogs, nasal cavity, trachea, oviduct of vertebrates.
  • Structure: Cells are cuboidal or columnar. Free ends of the cells have hair-like cilia; the basal end rests on a basement membrane. Oval nucleus located at the basal end.
  • Function: Creates movement of materials in a specific direction, e.g., preventing foreign particles from entering the trachea, moving ovum through the oviduct.
 (v) Glandular Epithelium
  • Structure: Cells can be columnar, cuboidal, or pyramidal. Large nucleus situated at the base with secretory granules in the cytoplasm. Glands can be unicellular (e.g., goblet cells) or multicellular (e.g., salivary glands).
  • Types: Exocrine glands: Secrete substances at specific sites (e.g., salivary gland, sweat gland). Endocrine glands: Release secretions directly into the bloodstream (e.g., thyroid gland, pituitary gland).
  • Function: Secretes mucus, enzymes, and hormones; lubricates inner surfaces of respiratory and digestive tracts.

(vi) Sensory Epithelial Tissue

  • Location: Nose (Olfactory), ear (Auditory hair cells), eye (Photoreceptors).
  • Structure: Composed of modified columnar cells and elongated neurosensory cells. Sensory hairs are present at the free end.
  • Function: Perceives external and internal stimuli.
 (vii) Germinal Epithelium
  • Function: Cells divide meiotically to produce haploid gametes (e.g., lining of seminiferous tubules, inner lining of ovary).
Compound Epithelium
  • Structure: Consists of many layers of cells; only the lowermost layer rests on the basement membrane.
 (i) Stratified Epithelium
  • Structure: Nucleus in the basal layer (stratum germinativum). Cells at the free surface become flat and lack nucleus (stratum corneum).
  • Function: Protection (e.g., epidermis of skin, oesophagus, cornea, vagina, rectum).

(ii) Transitional Epithelium

  • Structure: Similar to stratified epithelium, but cells can change shape depending on the degree of stretch. Cells transition from round/globular to thin/flat as tissue stretches.
  • Function: Allows distension of organs (e.g., urinary bladder).

Distinction Between Simple Epithelium and Compound Epithelium

Cell Junctions
  • Cell Junctions: Epithelial cells are connected to each other laterally and to the basement membrane by junctional complexes called cell junctions.

Types of Cell Junctions

  1. Gap Junctions (GJs): Intercellular connections allowing the passage of ions and small molecules. Enable the exchange of chemical messages between cells.
  2. Adherens Junctions (AJs): Involved in signaling pathways and transcriptional regulations.
  3. Desmosomes (Ds): Provide mechanical strength to epithelial tissue, cardiac muscles, and meninges.
  4. Hemidesmosomes (HDs): Enable strong adherence of cells to the underlying basement membrane. Help maintain tissue homeostasis through signaling.
  5. Tight Junctions (TJs): Maintain cell polarity and prevent lateral diffusion of proteins and ions.

Connective Tissue

Definition: Connective tissue is a widespread tissue in the body that binds, supports, and strengthens other body tissues and organs.

Characteristics
  • Variety of Cells & Fibers: Contains different cells and fibers embedded in an abundant intercellular substance called the matrix.
  • Fibroblasts: Cells that form fibers.
  • Highly Vascular: Except for cartilage.
Types of Connective Tissue

1. Connective Tissue Proper: Loose Connective Tissue (e.g., Areolar and Adipose Tissue) & Dense Connective Tissue (e.g., Ligament and Tendon)

2. Supporting Connective Tissue (Skeletal Tissue): Cartilage & Bone

3. Fluid Connective Tissue: Blood & Lymph

Functions

  • Protection: Shields vital organs.
  • Packing Material: Acts as a filler between structures.
  • Healing: Assists in the healing process.
(A) Connective Tissue Proper

(1) Loose Connective Tissue (Matrix: Semisolid, jelly-like, viscous, composed of gelatin)

(i) Areolar Connective Tissue

Location: Under the skin, between muscles, bones, around organs, blood vessels, and the peritoneum.

Structure:

Fibers:
  • White Fibers: Made of collagen, providing tensile strength.
  • Yellow Fibers: Made of elastin, providing elasticity.
Cells:
  • Fibroblasts: Large, flat cells with branching processes; produce fibers and polysaccharides for the matrix.
  • Mast Cells: Oval cells that secrete heparin and histamine.
  • Macrophages: Amoeboid, phagocytic cells.
  • Adipocytes (Fat Cells): Store fat with an eccentric nucleus.

Function: Acts as a packing material, aids in healing, and connects different organs or tissue layers.

(ii) Adipose Tissue (adipo = fat)

Location: Found with areolar connective tissue, beneath the skin, around kidneys, and between internal organs.

Structure:

  • Contains many adipocytes (fat-storing cells).
  • Cells are rounded or polygonal.
  • Nucleus is shifted to the periphery due to fat storage.
  • Matrix is sparse with few fibers and blood vessels.

Types:

  1. White Adipose Tissue: Opaque due to many adipocytes. Common in adults.
  2. Brown Adipose Tissue: Reddish-brown due to many blood vessels.

Functions:

  • Insulator: Retains body heat, aiding survival in cold regions.
  • Shock Absorber: Cushions organs.
  • Energy Source: Stores fat for energy.
  • Found in soles, palms, and around organs like kidneys.

(2) Dense Connective Tissue
  • Structure: Fibers and fibroblasts are tightly packed in the matrix.
  • Types:
  • Dense Regular Connective Tissue: Collagen fibers arranged parallel. Example: Tendons and Ligaments.
  • Dense Irregular Connective Tissue: Fibers and fibroblasts arranged randomly. Example: Dermis of skin.
Tendons
  • Definition: A type of dense regular connective tissue.
  • Function: Connects skeletal muscles to bones.
  • Structure: Contains bundles of white fibers for tensile strength. Example: Achilles tendon (connects calf muscles to heel bone).
Key Points:
  • Achilles tendon: The largest and strongest tendon in the body.
  • Function: Allows standing on toes when calf muscles flex.
  • Injury: Common in athletes, indicated by pain in the ankle or lower calf.
Ligaments
  • Definition: A type of dense regular connective tissue made up of elastic fibers.
  • Location: Found at joints.
  • Function: Prevents dislocation of bones by holding them together.
(C) Supporting Connective Tissue
  • Definition: Characterized by the presence of a hard matrix.
  • Types: Cartilage & Bone
(i) Cartilage

Structure:

  • Matrix called chondrin is enclosed by perichondrium (a sheath of collagenous fibers).
  • Chondroblasts (immature cells) mature into chondrocytes.
  • Chondrocytes are found in lacunae (small cavities in the matrix).
  • Each lacuna contains 2 to 8 chondrocytes.
  • Cartilage forms the endoskeleton of cartilaginous fish like sharks.

Types of Cartilage:

1. Hyaline Cartilage:

  • Elastic and compressible.
  • Perichondrium is present.
  • Matrix is bluish-white and gel-like with fine collagen fibers.
  • Location: Ends of long bones, epiglottis, trachea, ribs, larynx, hyoid.
  • Function: Acts as a shock absorber, provides flexibility, and reduces friction.

2. Elastic Cartilage:

  • Perichondrium is present.
  • Matrix contains elastic fibers; fewer chondrocytes.
  • Location: Ear lobe, tip of the nose.
  • Function: Provides support and maintains shape.
 3. Fibrocartilage:
  • Most rigid type of cartilage.
  • Perichondrium is absent.
  • Matrix contains bundles of collagen fibers; few scattered chondrocytes.
  • Location: Intervertebral discs, pubic symphysis.
  • Function: Maintains position of vertebrae.

4. Calcified Cartilage:

  • Becomes rigid due to salt deposition in the matrix.
  • Function: Reduces joint flexibility in old age.
  • Example: Head of long bones.

Bone
  • Matrix: Rigid and non-pliable, made up of ossein (contains calcium salt hydroxyapatite).
  • Periosteum: A tough outer membrane that encloses the matrix.
  • Lamellae: Concentric layers within the matrix.
  • Vascularization: Bones are well-vascularized with blood vessels and nerves that pierce the periosteum.
  • Comparison with Cartilage: Unlike cartilage, which is thin, avascular, and flexible, bones are stronger due to their dense and rigid matrix.
Types of Bones:

1. Spongy Bones:

  • Haversian System: Absent.
  • Matrix: Arranged in a rectangular pattern forming trabeculae.
  • Red Bone Marrow: Present within the spaces of the trabeculae.

2. Compact Bones:

  • Haversian System: Present without any spaces between the lamellae.
  • Matrix: Dense and tightly packed.
Functions of Bones:
  • Support and Protection: Provides structural support and protection to various organs.
  • Movement: Facilitates movement by acting as levers for muscles.
Histological Structure of Mammalian Bone:

Matrix:

  • Called ossein, composed of mineral salt hydroxyl apatite.
  • Enclosed by the periosteum.
  • Arranged in concentric layers known as lamellae.

Lamellae:

  • Contain fluid-filled cavities called lacunae.
  • Canaliculi: Fine canals radiating from lacunae, connecting adjacent lamellae.

Bone Cells:

  • Osteoblasts: Active bone-forming cells found in the lacunae.
  • Osteocytes: Inactive bone cells also located in the lacunae.

Haversian System:

  • Characteristic feature of mammalian bone.
  • Haversian Canal: Contains an artery, vein, and nerves, and is surrounded by lamellae.
(D) Fluid Connective Tissue (Vascular)
  • Components: Blood and lymph are the primary fluid connective tissues in the body of animals.

Muscular Tissue

  • Muscle Fibers: The cells of muscular tissue are elongated and are called muscle fibers.
  • Sarcolemma: A membrane that covers the muscle fibers.
  • Sarcoplasm: The cytoplasm of muscle cells.
  • Myofibrils: Large numbers of contractile fibrils present within the sarcoplasm. These are responsible for muscle contraction.
  • Nuclei: Depending on the muscle type, there may be one or multiple nuclei per muscle fiber.
  • Proteins: Myofibrils are composed of the proteins actin and myosin, which are crucial for muscle contraction.
  • Contractility: Muscle fibers contract and decrease in length upon stimulation, which is why muscular tissue is also referred to as contractile tissue.
  • Vascularization: Muscular tissue is well-supplied with blood vessels.
  • Innervation: Muscular tissue is innervated by nerves, allowing it to respond to stimuli.
  • Mitochondria: Muscle cells contain a large number of mitochondria to meet their high energy demands.
Types of Muscular Tissue:

1. Skeletal Muscles / Striated Muscles / Voluntary Muscles:

  • Location: Found attached to bones.
  • Function: Responsible for voluntary movements.

2. Smooth Muscles / Non-striated Muscles / Involuntary Muscles:

  • Location: Found in the walls of visceral organs (like the stomach, intestines) and blood vessels.
  • Function: Control involuntary actions such as the movement of food through the digestive system.

3. Cardiac Muscles:

  • Location: Found in the walls of the heart (myocardium).
  • Function: Responsible for the rhythmic contractions of the heart that pump blood throughout the body.
Muscular Tissue

(i) Skeletal Muscles:

Overview: Skeletal muscles, also known as voluntary muscles, are the most abundant type of muscle in the human body, with over 650 named muscles.


Location: Found attached to bones.

Structure:

  • Fasciculi: Consist of a large number of fasciculi, which are bundles of muscle fibers.
  • Epimysium: Fasciculi are wrapped by a connective tissue sheath called epimysium or fascia.
  • Perimysium: Each fasciculus is individually covered by perimysium.
  • Myofibers: Each fasciculus contains many muscle fibers called myofibers.
  • Sarcolemma: The cell membrane of the muscle fiber.
  • Sarcoplasm: The cytoplasm of the muscle fiber, containing many parallel myofibrils.
  • Myofibrils: Each myofibril is made up of repeated functional units called sarcomeres.'
  • Striations: The arrangement of dark and light bands gives skeletal muscles a striated appearance.
Sarcomere: The functional unit of skeletal muscles, consisting of:
  • A band (Anisotropic band): Contains the contractile proteins actin and myosin.
  • H zone: A light area in the center of the A band.
  • M line: Located in the center of the H zone.
  • I bands (Isotropic bands): Light bands containing only actin.
  • Z line: Separates adjacent I bands and is where actin filaments are anchored.

Functions: Skeletal muscles produce quick, strong, voluntary contractions, enabling voluntary movements of the body.

Types of Skeletal Muscles:

  • Red Muscle: High myoglobin content, rich in oxygen, suitable for endurance activities.
  • White Muscle: Low myoglobin content, better for short bursts of power.

Myoglobin: Myoglobin is a red-colored, iron-containing pigment found in muscles, capable of carrying one molecule of oxygen. It allows muscles to source oxygen from both myoglobin and hemoglobin.

(ii) Smooth or Non-striated Muscles:

Overview: Also known as visceral muscles or involuntary muscles due to their location and function.

Structure:

  • Spindle-shaped cells: Muscle cells are spindle-shaped or fusiform, with a single, centrally located nucleus.
  • Unbranched fibers: Fibers are unbranched and lack striations.
  • Myofibrils: Contain contractile proteins actin and myosin, with more actin than myosin.
  • Autonomous nervous system: These muscles are controlled by the autonomic nervous system.

Location: Found in the walls of visceral organs (such as the digestive system) and blood vessels.

Function: Involved in involuntary movements, such as the peristaltic movement of food through the digestive system.

(iii) Cardiac Muscles:

Overview: Cardiac muscles exhibit characteristics of both striated (skeletal) and non-striated (smooth) muscle fibers.

Structure:

  • Uninucleate fibers: Each fiber has a single nucleus, but the fibers appear multinucleate due to their branching.
  • Branched appearance: Adjacent muscle fibers join together, giving the muscle a branched appearance.
  • Intercalated discs: Transverse thickenings of the sarcolemma form intercalated discs, which are points of adhesion between muscle fibers. These discs help synchronize the contraction of the cardiac muscle cells.

Location: Found in the wall of the heart (myocardium).

Function: Cardiac muscles are responsible for the rhythmic contraction and relaxation of the heart, which is essential for circulating blood throughout the body.

Myogenic Heart vs. Neurogenic Heart

Myogenic Heart:

  • Definition: A heart that generates its own impulses for contraction.
Characteristics:
  • The cardiac muscles in mammals are modified to generate electrical impulses autonomously.
  • The impulse is initiated within the heart muscle itself without needing external neural stimulation.
  • Example: The human heart is a myogenic heart.

Neurogenic Heart:

  • Definition: A heart that requires neural stimulation to initiate contractions.
Characteristics:
  • The cardiac muscles require impulses from the nervous system to contract.
  • This type of heart is regulated by neural signals from the autonomic nervous system.
  • Example: Some invertebrates, like certain crustaceans, have neurogenic hearts.
Nervous Tissue

Characteristics:

  • Components: Composed of nerve cells (neurons) and supporting cells (neuroglia).
  • Matrix: Lacks an extracellular matrix.

Neurons:

  • Function: Structural and functional units of the nervous system responsible for transmitting impulses.
  • Characteristics: Excitability: Ability to change membrane potential in response to stimuli. Conductivity: Ability to transmit impulse waves from one part of the neuron to another.

Neuroglial Cells:

  • Function: Support, nourish, and protect neurons.
  • Characteristics: Non-neuronal cells that can regenerate and divide, filling the spaces between neurons.

Structure of a Neuron:

Cyton (Cell Body):

  • Contains neuroplasm (granular cytoplasm) with organelles such as mitochondria, Golgi apparatus, rough endoplasmic reticulum (RER), and Nissl’s granules (sites of protein synthesis).
  • Contains a centrally located nucleus.

Processes:

  • Dendrons: Short, branched extensions that receive and carry impulses toward the cell body. Fine branches of dendrons are called dendrites.
Axon: A single, elongated, cylindrical process that transmits impulses away from the cell body.
  • Axolemma: Membrane surrounding the axon.
  • Axoplasm: Cytoplasm within the axon, rich in mitochondria and neurofibrils.
  • Myelin Sheath: Fatty layer covering the axon, produced by Schwann cells; provides insulation and increases impulse conduction speed.
  • Neurilemma: Outer covering of the myelin sheath, also part of Schwann cells.
  • Node of Ranvier: Gaps in the myelin sheath where the axon is exposed.
  • Telodendron: Fine branching at the axon's end, involved in synaptic transmission.

Nissl’s Granules:

  • Description: Large granular bodies found in the cytoplasm of neurons.
  • Composition: Made up of rough endoplasmic reticulum (RER) and free ribosomes.
  • Function: Sites of protein synthesis, essential for neuron function and maintenance.

Classification of Neurons

Based on Function:

1. Afferent Neuron (Sensory Neuron):

  • Function: Carries impulses from sensory organs to the central nervous system (CNS).
  • Location: Found in the dorsal root of the spinal cord.
  • Characteristics: Transmits sensory information like touch, temperature, and pain.

2. Efferent Neuron (Motor Neuron):

  • Function: Carries impulses from the CNS to effector organs such as muscles and glands.
  • Location: Found in the ventral root of the spinal cord.
  • Characteristics: Responsible for initiating and controlling movement and glandular secretion.

3. Interneuron (Association Neuron):

  • Function: Processes and integrates sensory impulses and activates the appropriate motor neurons to generate a motor response.
  • Location: Found between sensory and motor neurons, primarily in the CNS.
  • Characteristics: Acts as a relay and processing unit for signals within the CNS.

Based on Presence or Absence of Myelin Sheath:

1. Myelinated Nerve Fibres (Medullated Nerve Fibres):

  • Myelin Sheath: An insulating fatty layer around the axon, making the fibres appear white.
  • Nodes of Ranvier: Present at regular intervals along the axon.
  • Inter-nodes: Present between nodes.
  • Conduction: Saltatory conduction occurs, which speeds up nerve impulse transmission.
  • Speed: Conducts nerve impulses faster.
  • Schwann Cells: Secrete the myelin sheath.
  • Examples: Cranial nerves of vertebrates.

2. Non-Myelinated Nerve Fibres (Non-Medullated Nerve Fibres):

  • Myelin Sheath: Absent.
  • Nodes of Ranvier: Absent.
  • Inter-nodes: Absent.
  • Conduction: Continuous conduction, slower than myelinated fibres.
  • Speed: Conducts nerve impulses slower.
  • Appearance: Appears grey due to the absence of myelin.
  • Examples: Nerves of the autonomic nervous system.

Based on Number of Processes from Cyton:

1. Unipolar (Monopolar) Neuron:

  • Structure: Has a single process that splits into an axon and a dendron.
  • Function: Conducts impulses to the CNS.
  • Example: Neurons of the dorsal root ganglion of the spinal nerve.

2. Bipolar Neuron:

  • Structure: Has two processes, one dendron and one axon, originating from opposite poles of the cyton.
  • Function: Transmits special senses such as sight, smell, taste, and hearing.
  • Example: Neurons in the retina of the eye, olfactory epithelium.

3. Multipolar Neuron:

  • Structure: Star-shaped with more than two processes; one axon and multiple dendrites.
  • Function: Conducts impulses from receptors to the CNS and integrates sensory and motor information.
  • Example: Most neurons in the CNS and all motor neurons.
Classification of Neurons

Based on Function:

1. Afferent Neuron (Sensory Neuron)

  • Function: Carries impulses from sense organs to the Central Nervous System (CNS).
  • Location: Dorsal root of the spinal cord.

2. Efferent Neuron (Motor Neuron)

  • Function: Carries impulses from CNS to effector organs.
  • Location: Ventral root of the spinal cord.

3. Interneuron (Association Neuron)

  • Function: Processes and integrates sensory impulses, activates motor neurons.
  • Location: Between sensory and motor neurons.

Based on Presence of Myelin Sheath:

1. Myelinated Nerve Fibres (Medullated)

  • Myelin Sheath: Insulating fatty layer around the axon.
  • Nodes of Ranvier: Present at intervals.
  • Inter-nodes: Present.
  • Conduction: Saltatory conduction (faster impulse transmission).
  • Color: Appears white.
  • Example: Cranial nerves of vertebrates.

2. Non-Myelinated Nerve Fibres (Non-medullated)

  • Myelin Sheath: Absent.
  • Nodes of Ranvier: Absent.
  • Inter-nodes: Absent.
  • Conduction: Slower impulse transmission.
  • Color: Appears grey.
  • Example: Nerves of the autonomous nervous system.

Based on Number of Processes:

Unipolar (Monopolar) Neuron

  • Processes: One process from the cyton (both axon and dendron at one point).
  • Function: Conducts impulses to CNS.
  • Example: Neurons of dorsal root ganglion of spinal nerve.

Bipolar Neuron

  • Processes: Two processes from the cyton (one dendron and one axon at opposite poles).
  • Function: Transmits special senses (sight, smell, taste, hearing).
  • Example: Neurons of retina of the eye, olfactory epithelium.

Multipolar Neuron

  • Processes: More than two processes (one axon and multiple dendrons).
  • Function: Conducts impulses from receptors to CNS, integration between sensory and motor neurons.
  • Example: Most neurons in the CNS and all motor neurons.
Transmission of Impulse Between Neurons

Synapses: Junctions where nerve impulses are transmitted from one neuron to another.

Components:
  • Pre-synaptic Neuron: The neuron sending the impulse.
  • Post-synaptic Neuron: The neuron receiving the impulse.
  • Synaptic Cleft: Gap that may separate the pre- and post-synaptic neurons.

Types of Synapses:

Electrical Synapses

  • Structure: Membranes of neurons are very close together.
  • Function: Electrical current flows directly from one neuron to another.
  • Speed: Faster impulse transmission.

Chemical Synapses

  • Structure: Membranes are separated by a synaptic cleft.
  • Mechanism:
  • Neurotransmitters: Chemicals involved in impulse transmission.
  • Axon Terminals: Contain vesicles with neurotransmitters.
  • Process:
  • Impulse arrival at axon terminal triggers neurotransmitter release.
  • Neurotransmitters cross the synaptic cleft and bind to receptors on the post-synaptic membrane.
  • Binding opens ion channels, generating a new potential in the post-synaptic neuron.
Structure of a Nerve

Components:

  • Axons: Multiple axons are present within a nerve.
  • Myelin Sheath: Fatty coating surrounding axons.

Layers of Connective Tissue:

  • Endoneurium: Surrounds each axon (innermost layer).
  • Fasciculi: Bundles of axons with their endoneurium.
  • Perineurium: Wraps each fascicle (middle layer).
  • Epineurium: Outermost protective layer surrounding the nerve and fascicles.

Blood Supply: Perineurium and Epineurium: Contain blood vessels providing nutrition to the nerve.