Nervous system

what is the role of communication in an organisms survival

to respond to changes in the internal or external environment

essential for homeostasis and to allow rapid response to threat or danger

give examples of an organisms internal environment

temperature

pH

blood pressure

internal pain

give examples of an organisms external environment

temperature

sound

light

pH

what communication systems do multicellular animals have

nervous system

endocrine system (hormones)

what communication systems do plants have

chemical communication systems using plant hormones

what is the role of sensory neurones

transmit impulses from a sensory receptor cell to a relay neurone, motor neurone or the brain

what is the role of motor neurones

transmit impulses from a relay/sensory neurone to an effector

what is an effector

a muscle or gland

what is the role of a relay neurone

transmit impulses between neurones

what is the typical electron impulse pathway

receptor→ sensory neurone→ relay neurone→ motor neurone→ effector

describe the structure of a myelin sheath

many layers of plasma membrane

produced from schwann cells- grows around the axon many times

what is the role of a myelin sheath

insulating layer- allows myelinated neurones to conduct the electrical impulses at a much faster rate

describe nodes of ranvier

creates gaps in the myelin sheath- enables electrical impulses to jump from one node to the next- increases speed of transmission

in unmyelinated neurons impulses dont jump- instead travels continuously which is much slower

describe the cell body

contains the nucleus- surrounded by cytoplasm

describe the cytoplasm in the cell body

large amount of endoplasmic reticulum and mitochondria- involved in the production of neurotransmitters

what are neurotransmitters

chemicals used to pass signals from one neuron to the next

describe dendrons

short extensions which come from the cell body

divide into smaller branches- dendrites

responsible for transmitting electrical impulses towards the cell body

describe axons

single, elongated nerve fibres that transmit impulses away from the cell body

fibre is cylindrical in shape - consists of narrow regions of cytoplasm- surrounded by cell membrane

what are neurones

specialised cells that transmit information in the form of action potentials

what are glial cells

help neurones get nutrients from blood and some schwann cells insulate axons

what is included in the peripheral ns

nerves running between cns and rest of the body

motor and sensory neurons

what is the white matter in the brain

myelinated areas- fat

what is the grey area of the brain

the cell bodies of neurons

what are meninges

membranous covering of the brain and spinal cord

what is the role of the cerebrospinal fluid

protect brain and spinal cord from trauma

supply nutrients to nervous system tissue

remove waste products from cerbral metabolism

how is the spinal cord protected

vertebral column

cerebrospinal fluid

describe the location of spinal nerves

go to/from the spinal cord

describe the location of cranial nerves

go to/from the brain

what makes up the structure of spinal nerves

bundles of sensory and motor neurones

which ns are included in peripheral ns

somatic and autonomic

describe the somatic ns

voluntary

sensory and motor- run to skeletal muscles

motor neurones cell bodies are located in the cns

describe the autonomic ns

2 sets motor neurones carry impulses to effectors - not to skeletal muscles

cell bodies are located outside the cns in autonomic ganglions

actions from autonomic are not under conscious control

what is included in the autonomic ns

sympathetic

parasympathetic

describe the sympathetic division of autonomic ns

occurs at times of stress

stimulatory

increased hr, dilated pupils, reduces digestive activity

uses noradrenaline

describe the parasympathetic division of autonomic ns

active during sleep or relaxation

inhibitory

decreases hr, constricts pupils, increases digestive activity

uses acetylcholine

what are the structural differences between autonomic and somatic ns

connections between multiple motor neurones

different neurotransmitters

where myelination occurs and extent to that myelination

the type of tissue each stimulates/inhibits

how is hr controlled in the sympathetic ns

transmitted through accelerator nerve

how is hr controlled in the parasympathetic ns

transmitted via vagus nerve

what controls the increase/decrease of hr

baroreceptors and chemoreceptors

what is a reflex action

an immediate short lives response to a stimulus

involuntary

what is a reflex arc

composed of various structures along which impulses travel during a reflex action

describe the blinking reflex

involuntary

cranial reflex

rapid

occurs when the cornea is stimulated

describe the optical reflex

response to very bright lights

protects lense and retina

what is the purpose of the blinking reflex

to keep the cornea safe from damage- such as from foreign bodies

describe the blinking reflex response to foreign bodies

impulse sent along sensory neuron

passed to relay neuron in the lower brains tem

impulse sent along branches of motor neuron- initiates a motor response to close eyelids

why do doctors test the blinking reflex

on unconscious patients

if response is present- lower brain stem is functioning - cannot be diagnosed as brain-dead

what is the survival importance of reflexes

avoid the body being harmed/reduce severity of damage

how do reflexes increase chances of survival

involuntary- very quick as the reflex arc is v short

present from birth- immediate protection

used in everyday actions- e.g. staying stood up and not falling over

describe the knee jerk reflex

spinal reflex

neural circuit only goes up to the spinal cord- not to the brain

purpose is to maintain posture and balance

how is the knee jerk reflex arc initiated

when the leg is tapped below the patella it stretches the patella tendon- acts as a stimulus

describe the reflex arc of the knee jerk

extensor muscle on top of the thigh contracts

relay neurone inhibits the motor neuron of the flexor muscle- causes it to relax

contraction co-ordinated with the relaxation of the antagonistic flexor hamstring muscle

leg kicks

what is homeostasis

functions of organs must be coordinated to maintain a constant internal enviornment

what are the 2 main features of sensory receptors

specific to a single type of stimulus

act as a transducer- convert a stimulus into a nerve impulse

what are the types of sensory receptors in animals

mechanoreceptor

chemoreceptor

thermoreceptor

photoreceptor

describe mechanoreceptors

stimulus- pressure and movement

e.g. of sense organ- skin

describe chemoreceptors

stimulus - chemicals

e.g. of sense organ- nose

describe thermoreceptors

stimulus- heat

e.g. of sense organ- tounge

describe photoreceptors

stimulus- light

e.g. of sense organ- eye

describe sensory receptor role as a transducer

receptor converts the stimulus into a nervous impulse- called a generator potential

describe the role of pacinian corpuscle

specific sensory receptors that detect mechanical pressure

located deep in skin- most abundant in fingers and soles of feet

found within joints- so you know which joints are changing direction

describe the structure of pacinian corpuscle

end of sensory neuron is in the centre- surrounded by layers of connective tissue- each layer is separated by a layer of gel

within membrane- sodium ion channels - stretch sodium channel- stretch and change shape

how does a pacinian corpuscle convert mechanical pressure into a nervous impulse

normal state- stretch sodium ion are too narrow to allow sodium ions to pass through - resting potential

pressure is applied- changes shape- causes membrane to stretch

sodium ion channels widen- sodium ions diffuse into neuron

influx of positive sodium ions changes potential of membrane- becomes depolarised

generator potential creates an action potential (nerve impulse) that passed along the sensory neuron

action potential is transmitted along neurons to the CNS

when does the resting potential occur

when a neuron is not transmitting an impulse

occurs because of the movement of sodium and potassium ions across the axon membrane

→ phospholipid bilayer prevents ions from diffusing across the membrane - so they have to be transported via channel proteins

describe the movement of sodium and potassium in/out of the axon

sodium ions actively transported out of the axon where potassium ions are actively transported into the axon

by the sodium- potassium pump

for every 3 sodium ions pumped out, 2 potassium ions are pumped in

describe the conc. of sodium and potassium ions in the axon

higher conc. of sodium ions in outer membrane than inside axon cytoplasm

more potassium ions inside the cytoplasm than outside

sodium ions diffuse back into the axon down electrochemical gradient - potassium ions diffuse out of the axon

what is the name given to a concentration gradient of ions

electrochemical gradient

describe sodium ion channels

most sodium gates channels are closed- prevents the movement of sodium ions

describe potassium ion channels

open- thus allowing potassium ions to diffuse out of axon

describe action potential

when a stimulus is detected by a sensory receptor and the energy of the stimulus temporarily reverse the charge of the axon membrane

potential difference across the membrane depolarises (negative to positive charge)

the impulse passes repolarization - positive back to negative charge

why does an action potential occur

when protein channels in the axon membrane change shape because of the change of voltage across the membrane

what events occur during an action potential

neurone at resting potential - potassium channels open, sodium channels closed

energy of stimulus triggers sodium gates to open- membrane is more permeable- sodium ions diffuse into axon

charge causes more sodium ion channels to open- more sodium in

when potential difference reaches +40mV - sodium ion channels close and potassium open

potassium ions diffuse out down electrochemical gradient- inside of axon becomes more negative

hyperpolarization - potassium channels close

axon returns to resting potential- repolarized

what is hyperpolarization

initially lots of potassium ions diffuse out of the axon- inside of axon is more negative than its normal resting state

describe propagation of action potentials

nerve impulse starts at one end of the neuron and is propagated along the axon to the other end of the neuron

what does repolarization require

ATP in the sodium pump

what is saltatory conduction

action potential jumping from one node to another

much faster than a wave of depolarisation

how does the axon diameter influence the speed of action potential

bigger=faster

less resistance to flow of ions in the cytoplasm

how does temperature influence action potential

higher temp= faster nerve impulse

ions diffuse faster at higher temps

after 40 degrees- proteins become denatured

what is the all or nothing principle

certain level of stimulus- the threshold value always triggers a response

no matter how large the stimulus is - same size action potential is triggered

if threshold isnt reached- no action potential is triggered

size of stimulus does affect number of action potentials generated in a given time