L4 - Nerve Flashcards
Nervous system subdivisions
- CNS: brain, spinal cord (and optic nerve)
- PNS: all nervous tissue outside CNS
Nervous system function
- Maintain homeostasis (works closely along with endocrine system)
- Initiate voluntary movements
- Responsible for perception, behaviour and memory
Nervous tissue functions
- Sensory: detection of internal and external stimuli and transfer to CNS
- Integrative: analysis and storing of information
- Motor (effector): stimulation of effectors (muscle and glands) through PNS - Control muscle activity, Regulate glandular secretions
Nervous tissue composition
Two types of cells:
1) neurons
2) neuroglia
Neuron features
- Can be very large - longest cells in the body (up to 1 m - spinal cord to toe)
- Conscious and unconscious control
- Sensitive to stimuli - convert stimuli to electrical signals (action potentials)
- Do NOT divide (once damaged, they’re damaged)
- High metabolic rate (die rapidly without oxygen)
Neuron structural components
Dendrites, axon, cell body (soma/perikaryon), cytoskeleton
Dendrite appearance
Short, tapering, highly branched
Dendrite function
Receiving/input part of the neuron - convey nerve impulses into cell body
Axon appearance
Long, single, thin, cylindrical
Axon function
Output portion of the neuron - carries nerve impulses away from neuron/cell body
Axon composition
Axoplasm, axolemma
Cell body/soma/perikaryon
Contains nucleus and organelles
Cytoskeleton composition
Neurofibrils, Microtubules (, Lipofuscin)
Neurofibrils
bundles of intermediate filaments that provide cell shape and support
Microtubules
assist moving materials between cell body and axon
Lipofuscin
pigment occurring as yellowish brown granule clumps in aging neurons
- Product of neuronal lysosomes that accumulate as neuron ages but doesn’t seem to harm neuron
Structural classification of neurons
Multipolar, bipolar, unipolar, anaxonic
Multipolar. Features
Some of longest (spinal cord to toes muscles)
Multipolar. Structure
- multiple dendrites
- single axon
- cell body among (centre of) dendrites
Multipolar. Location
- Most common neurons in CNS (brain, spinal cord)
- All motor neurons which control skeletal muscles
Bipolar. Features
Rare and small (30 µm)
Bipolar. Structure
- single dendrite (can branch at tip but not at the cell body)
- single axon
- cell body between axon and dendrite
Bipolar. Location
Special sense organs (sight - retina of eye, smell - olfactory area of brain, hearing - inner ear)
- Relay information from receptor to neurons
Unipolar. features
- Very long (1 m) like motor nerves from CNS to toe tip (periphery back to CNS)
- Begin as bipolar neurons in embryo and then dendrites and axon fuse together during development
Unipolar. Structure
- Dendrites and axon are continuous (whole thing from where dendrites converge is the axon)
- cell body is off to one side
Unipolar. Location
Most sensory nerves (touch, pressure, pain, thermal)
Types of sensory receptors
Corpuscle of touch, type 1 cutaneous mechano-receptor, lamellated receptor, nociceptor
Corpuscle of touch
- touch receptor
- Mass of dendrites enclosed by capsule of connective tissue
Type 1 cutaneous mechano-receptor
- touch receptor
- Free nerve endings (bare dendrites) that make contact with tactile epithelial cells of the stratum basale of skin
Lamellated receptor
- pressure receptor
- Multilayered connective tissue capsule encloses dendrite