Brain & Nervous SystemChapter 15

Brain several main regions - (1)Cerebrum - responsible for thought,

reasoning, imagination etc. - (2) cerebellum - controls balance & co-

ordination - (3) medulla - controls breathing & heart rate - (4) hypothalamus - regulates water balance &

body temperature - (5) pituitary gland - releases many hormones (e.g.

ADH)

(2)

(3)

(1)

(5)(4)

Cerebrum Made of 2 hemispheres Each split into different regions E.g. sensory & motor strips Sensory areas receive impulses

from sense receptors The more receptors the body

part has, the bigger the sensory area

The impulses are interpreted and a response passed to the motor areas

The more mobile the body part, the larger the motor area

Both illustrated by a homunculus

Homunculus

SENSORY MOTOR

Organisation of the nervous system

Brain, spinal cord, and nerves = Central Nervous System (CNS)

Nerve cells are called neurones Neurones consist of a cell body

attached to nerve fibres The synapse is the space

between two neurones A sensory fibre takes impulses

towards the CNS A relay neurone passes the signal

along the CNS An axon fibre (motor neurone)

that takes the response away

Relay neurone

Reflex Action Reflex is a rapid, involuntary

response e.g. hand contacting a hot surface 1) Pain receptors in the skin

detect heat 2) Impulse sent along sensory

neurone 3) Impulse crosses synapse to

relay neurone & is passed along 4) Impulse crosses synapse to

motor neurone 5) Motor neurone takes response

signal to the axon endings 6) Signal is passed to the arm

muscles & arm lifts

Regulating body temperature

Hypothalamus - the body’s temperature

monitoring centre Receives nerve impulses from

thermoreceptors in the skin - to keep body shell at around 33oC Also contains central

thermoreceptors - detect blood temp changes - keeps core temp at 37oC Hypothalamus responds by sending

motor nerve impulses to effectors

Role of the skin Acts in response to the

hypothalamus ‘Too hot’ - Promotes heat

loss: 1) Increases sweating - converts water in sweat to

water vapour 2) Vasodilation (arterioles get bigger) - more blood flows to the

skin surface - more heat lost by radiation

Role of the skin (ctd.) ‘Too cold’ - Corrects

overcooling: - Decreases rate of sweating - Vasoconstriction (arterioles become

narrower) - Less blood flow to skin

surface - less heat lost by radiation - Erector muscles contract,

hairs raised - layer of air trapped next to

skin

Other Effectors Skeletal muscles undergo

brief, repeated contractions – SHIVERING In the liver, metabolic

reactions are increased - both help increase heat

production

Temperature control is an example of Negative Feedback Control