the nervous system

the nervous system

the nervous system

detects changes in the body, processes and stores information, initiates responses

stimulus

a detectable change in internal/external environments

sensory receptors

detect energy and convert it to electrical impulses which travel along neurones and initiate a response

CNS

the brain and spinal chord, processes information from the stimulus surrounded by a protective membrane called meninges, white matter = nerve fibres surrounded by myelin, grey matter is non myelinated nerve fibres

PNS

somatic nervous system, branched nerves from the CNS, sensory neurones carrying impulses from receptors to motor neuroses, autonomic nervous system, unconscious control of functions of internal organs

reflex action

rapid automatic response resulting from nervous impulses initiated by a stimulus, action involuntary and generally protective

sequence of the reflex arc

stimulus to receptor to sensory neurone to relay neurone to motor neurone to effector to response

nerve nets

the simplest form of the nervous system, seen in animals from early fossil records, a network of cells forming ganglia

ganglion cells

provide connections in several directions

sensory cells

detect stimuli

neurones

specialised cells adapted to carry impulses around the body

sensory neurone

impulses from sense receptors to the CNS

motor neurones

carry impulses from the CNS to the effector

relay neurones

receive impulses and transmit them to motor neurone

dendrite

thin fibres carrying impulses towards the cell body

axon

carries impulses away from the cell body

Schwann cells

surround and support nerve fibres, multi layered phospholipid

myelin sheath

electrical insulator quickens impulse transmission

nodes of ranvier

gaps in myelin sheath, exposes membrane, allows rapid impulse transmission

synaptic knob

swelling at the end of axon synthesising neurotransmitter

axon terminal

secretes neurotransmitters, transmits impulse to adjacent neurone

resting potential

potential difference along a membrane and how it is changed, membrane polarised, inside negative compared to outside

action potential

transmission of impulses along nerves, membrane depolarised and then repolarised, then hyperpolarised before resting potential ion balance is restored

how action potential travels

moves along axon, depolarising adjacent sections, a self perpetuating wave of depolarisation.

absolute refractory period

occurs at the site of the initial impulse, ion channels inactivated until resting potential is restores to ensure the impulse travels in one direction only

all or nothing theory

if intensity of the stimulus is below the threshold value then no action potential is initiated, a higher intensity of a stimulus does not give a greater action potential, it only increases the frequency of action potentials, prevents the brain from becoming overloaded with information

effect of temperature

ions move faster at a higher temp, warm blooded animals transmit impulses faster with better responses

diameter of axon

greater diameter means a greater area of membrane so impulses are faster, non-myelinated axons have a smaller diameter so there is a slower transmission of nerve impulses

myelination

insulates axon so speeds up transmissions, saltatory conduction, makes impulse faster

the synapse

separates neurones and sends impulses in one direction

electrical synapse

3nm across, small enough that impulse transmits directly from one to the next

chemical synapse

20nm gap, needs branches of axons to lie close to dendrites but not touch, neurotransmitter transmits impulse through a chemical diffusing along a synaptic cleft, generates a new impulse from a pre-synaptic membrane of one neurone to the post synaptic membrane of the next

synaptic transmission

arrival of impulse opens calcium channels, calcium diffuses in, causes synaptic vesicles to fuse with presynaptic membrane, releasing neurotransmitter acetylcholine into synaptic cleft, bonds to intrinsic protein and attaches, changes receptor protein shapes to open sodium channels and initiate a new impulse

removal of acetylcholine

direct uptake into presynaptic neurone, calcium ions actively transported out preventing further exocytosis, hydrolysis of acetylcholine by acetylcholinesterase, energy required to reform acetylcholine and for exocytosis

properties of synapses

transmit info, junctions which pass impulses in one direction, protect from overstimulation, filters out low level stimuli

temporal summation

general build up of depolarisation

spatial summation

pre synaptic neurones with the same post synaptic neurone, growing depolarisation and generating a large enough action potential

effects of drugs

act as synapses, disrupt function of neurotransmitters, produce abnormal impulses

sedatives

inhibit nervous system creating fewer action potentials

stimulants

stimulate nervous system allowing more action potentials

physchoactive drugs

alters brain function, changes could be advantageous leading to overuse