ANHB1102 Lecture Notes - Lecture 1: Axon Hillock, Peripheral Nervous System, Autonomic Nervous System
25 May 2018
School
Course
Professor
Nervous System:
-The nervous system is very complex and is the foundation of our conscience experience,
personality and behaviour
CNS and PNS: the principle divisions of the nervous system:
-Central Nervous System:
-Brain and spinal cord enclosed by cranium and vertebral column (bony boundaries) and
protected by meninges (specialised tissue that wraps around entire CNS)
-Tract: group of axons in CNS
-Peripheral Nervous System:
-All the nervous system except the brain and spinal cord; composed of nerves and ganglia
-Nerve; a bundle of fibres (axons) wrapped in fibrous connective tissue
-Ganglion; a knot-like swelling in a nerve where neuron cell bodies are concentrated
Sub-divisions of the Nervous System:
-Grey Matter; neuron cell bodies + glia
-White Matter; myelinated axons + glia
Control Systems:
-Molecular messengers/chemical messengers
-Circulate within the blood
-Most must freely pass through circulatory system
-Variable speed - generally slow
-Many aspects of control
-Different mechanisms
-Remembering earlier ‘experiences’; if experience has not been learnt - cannot create control
Overview of Nervous System:
1. Sense organs receive information about changes in the body and external environment, and
transmit coded messages to the brain and the spinal cord (CNS)
2. CNS processes information -> relates to past experiences -> determines appropriate response
3. CNS issues commands to muscle and gland cells to carry out such a response
E.g Hand on hot stove = temp receptors = inc in temp = pain = CNS = muscle contracts = move
hand away
Peripheral Nervous System (PNS):
-PNS contains sensory (feels) and motor (do) divisions within somatic (voluntary) and visceral
(involuntary) subdivisions
Motor; carries signals from CNS to effectors
(efferent)
Sensory; carries signals from receptors to CNS
(afferent)
Somatic; skeletal
muscles (involuntary
muscle contractions -
reflexes and voluntary)
Visceral; autonomic NS
(glands, cardiac and
smooth muscle) =
involuntary = visceral
reflexes
Somatic; receptors in
skin, muscle, bones and
joints
Visceral; viscera heart,
lungs, stomach, bladder
Sympathetic; (FIGHT OR FLIGHT) arouses
body for action, accelerating heartbeat and
respiration, while inhibiting digestive and
urinary systems
Parasympathetic; (REST AND DIGEST)
has a calming effect, slows heart rate and
breathing, stimulates urinary and digestive
systems
Transmission of Information:
-Along a single axon of a neuron
-Electrical transmission (very fast)
-Cell-cell communication
-Faster chemical release across narrow gaps between cells
Universal Properties of Neurons:
-Excitability (irritability); respond to environmental changes (stimuli)
-Conductivity; respond to stimuli by producing electrical signals that
are quickly conducted to other cells at distant locations
-Secretion (neurotransmitter release/response); when a electrical
signal reaches the end of a nerve fiber, the cell secretes a
chemical neurotransmitter that influences the next cell
Functional Classes of Neurons:
-Sensory (afferent) neurons: detect stimuli and transmit information
about them towards CNS
-Interneurons: lie entirely within CNS connecting motor and sensory
pathways. Receive signals from many newtons and decide
responses
-Motor (efferent) neurons: send signals out to muscles and gland cells
(the effectors)
Structure of a Neuron:
-Soma (cell body): control centre of neuron
-Has single, centrally located nucleus with large nucleolus
-Cytoplasm contains organelles
-Dendrites: branches off Soma (extension of plasma membrane)
-Primary site for receiving signals from other neurons
-More dendrites = more information received
-Provide precise pathways for reception and processing of
information
-Axon (nerve fiber): originates from a mound on soma called axon
hillock
-Axon is cylindrical, relatively unbranched for majority of length
-Takes information away from Soma
-Myelin sheath may enclose axon
-Terminal end: little swelling that forms a synapse (junction) with the next
cell
-Contains synaptic vesicles full of neurotransmitter
Morphological Classification of Neurons:
a) Multipolar (motor): short dendrites emanating from cell
body and one long axon
b) Bipolar (interneuron): have two main extensions of
similar length
c) Unipolar (sensory): neurons with short extensions that
quickly divide into two branches, one which functions
as a dendrite and the other as an axon
Difference Between Axon and Dendrite:
Fundamentals of Nerve Impulses:
-Resting Membrane Potential:
-Neuron not sending a signal it is ‘at rest’
-Inside= -ve, Outside= +ve
-At rest, K+ can cross membrane easily (Na+ cannot)
-Resting Potential of neuron = -70mV (inside is 70mV less than outside)
-More Na+ outside and more K+ inside
AXON
DENDRITE
Arise from axon hillock
Arise from receiving surface
Long and branched at distal end
Short and branched along length
Terminal branches form synaptic knob
No knobs formed
Contains vesicles with neurotransmitter
No vesicles
Carries impulses away from soma
Transmits impulses towards soma
Pre-synapse
Vesicle
Document Summary
The nervous system is very complex and is the foundation of our conscience experience, personality and behaviour. Cns and pns: the principle divisions of the nervous system: Brain and spinal cord enclosed by cranium and vertebral column (bony boundaries) and protected by meninges (specialised tissue that wraps around entire cns) All the nervous system except the brain and spinal cord; composed of nerves and ganglia. Nerve; a bundle of bres (axons) wrapped in brous connective tissue. Ganglion; a knot-like swelling in a nerve where neuron cell bodies are concentrated. Grey matter; neuron cell bodies + glia. Most must freely pass through circulatory system. Remembering earlier experiences"; if experience has not been learnt - cannot create control. E. g hand on hot stove = temp receptors = inc in temp = pain = cns = muscle contracts = move hand away. Pns contains sensory (feels) and motor (do) divisions within somatic (voluntary) and visceral (involuntary) subdivisions.
