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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
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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
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