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Brain & Nervous System

Brain & Nervous System. Chapter 15. Brain. several main regions - Cerebrum - responsible for thought, reasoning, imagination etc. - cerebellum - controls balance & co-ordination - medulla - controls breathing & heart rate - hypothalamus - regulates water balance & body temperature

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Brain & Nervous System

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  1. Brain & Nervous System Chapter 15

  2. Brain • several main regions • - Cerebrum • - responsible for thought, reasoning, imagination etc. • - cerebellum • - controls balance & co-ordination • - medulla • - controls breathing & heart rate • - hypothalamus • - regulates water balance & body temperature • - pituitary gland • - releases many hormones (e.g. ADH)

  3. Cerebrum • Made of 2 cerebral 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 it has • The impulses are interpreted and a response passed to the motor areas • The more mobile the body part, the larger the motor area it has • Both illustrated by a homunculus

  4. 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 • 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 • The synapse is the space between the end of one neurone and the beginning of another

  5. 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

  6. 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 thermoreceptorswhich detect blood temp changes • - keeps core temp at 37oC • Hypothalamus responds by sending motor nerve impulses to effectors

  7. Role of the skin • Acts in response to impulses from the hypothalamus • ‘Too hot’ - Promotes heat loss: • 1) Increases sweating rate by converting water in sweat to water vapour • 2) Vasodilation (arterioles get bigger) • - more blood flows to the skin surface(more heat lost as radiation)

  8. 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 is trapped next to the body

  9. Other Effectors • Skeletal muscles undergo brief, repeated contractions – SHIVERING • In the liver, metabolic reactions are increased • - both help increase heat production

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