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Brain & Nervous System

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 & Nervous System

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  1. Brain & Nervous System Chapter 15

  2. 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)

  3. 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

  4. Homunculus MOTOR SENSORY

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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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