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Brain & Nervous System. Chapter 15. Brain. (1). 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

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Brain
Brain

(1)

  • 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)

(4)

(5)

(2)

(3)


Cerebrum
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
Homunculus

MOTOR

SENSORY


Organisation of the nervous system
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 axonfibre (motor neurone) that takes the response away

Relay neurone


Reflex action
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
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
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
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
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