Understanding the Brain and Nervous System: Key Principles and Reflex Actions

1. Unit 3 Animal Physiology

2. Structure and Function of the Brain • The brain is a complex organ consisting of several different regions. • The CEREBRUM is the largest part of the brain and is divided into 2 connecting hemispheres. • The CEREBELLUM • The MEDULLA • The HYPOTHALAMUS

3. Structure and Function of the Brain cerebrum medulla cerebellum

6. Structure and Function of the Brain front rear Key: = motor area = sensory area

7. The cerebrum has discrete areas which perform their own functions distinct from the others Sensory area Receives information as sensory impulses from the body’s receptors e.g. sense organs. It then passes on to other parts of the brain to be analysed and interpreted. Motor area Consists of motor neurones which send out impulses to bring about appropriate voluntary movements of skeletal muscles.

8. Structure and Function of the Nervous System • The human nervous system is composed of 3 parts :- Brain, nerves and spinal cord. • The CENTRAL NERVOUS SYSTEM (CNS) is made up of just the brain and spinal cord. • Nerves carry electrical impulsesfrom the senses to the CNS and electrical impulses from the CNSto the muscles. • Nerves are made of bundles of fibres. Each nerve fibre is a part of a nerve cell or neurone. • - Stick the diagram into your jotter.

9. Types of Nerves 1) Sensory neurone Carries electrical impulses to the CNSfrom thesense organs 2) Motor neurone Carries electrical impulses from the CNS to the muscles and glands 3) Relay neurone Found in the spinal cord to connect sensory and motor neurones. • Stick in the diagram of the nerves

10. CNS Receptors e.g. sense organs Effectors e.g. muscles and glands stimuli response Flow of information Sensory nerves • The sense organs (receptors) detect a stimulus and send information to the CNS along sensory nerves. The brain sorts this information and sends instructions along motor nerves to the muscles (effector) to respond to that information Motor nerves

12. Reflex Arc • A reflex arc is the arrangement of the 3 different types of neurone. • ….starting with receptor; sensory neurone; relay neurone, motor neurone and effector. • Stick in the diagram of a reflex arc

13. Reflex Action • Transmission of a nerve impulse through a reflex arc results in a reflex action. • A reflex action is a rapid, involuntary, automatic response to a stimulus • A reflex action protects the body from damage. • They do not need conscious thought by the brain.

14. Examples of reflex actions • Limb withdrawal (stimulated by touching something sharp or hot), blinking, knee jerk, iris reflex and sneezing.

15. Arm extended at start Arm bends at end of reflex action

16. 1) Heat is detected by pain receptors in the skin 2) An impulse is immediately sent up the fibre of the sensory neurone. 3) In the grey matter of the spinal cord, the impulse crosses its 1st synapse (gap) 4) ..and passes through the relay neurone 5) The impulse crosses a 2nd synapse and passes into the motor neurone. 6) It then moves into the muscle (effector), chemicals are released and the muscle contracts moving the arm out of harm’s way.

17. Regulation of Body Temperature • The hypothalamus contains the body’s temperature-monitoring centre. • It receives nerve impulses from heat and cold receptors in the skin. The skin also acts as an effector. • It also has its own central thermoreceptors which monitors the temperature of the blood. • The central thermoreceptors detect changes in the body’s core temperature. • The hypothalamus responds to this info by sending motor nerve impulses to effectors.

18. The body core is the brain, lungs, gut and other vital organs – this is normally at 37°C. • The body shell is the skin, limbs, fat and skeletal muscle this is normally at around 33°C.

19. Overheating • The skin helps to correct overheating of the body by doing the following:- Increased rate of sweating By sweating a lot this lowers the body temperature Vasodilatation The arterioles leading to the skin become dilated which allows a large volume of blood to flow through capillaries near the skin surface. Heat can be lost as radiation.

20. Vasodilation

21. Overcooling • The skin helps to correct overcooling of the body by doing the following:- Decreased rate of sweating The rate you sweat reduces and stops the temperature from lowering any further. Vasoconstriction The arterioles leading to the skin become constricted which allows only small volume of blood to flow through capillaries near the skin surface. Little heat is lost by radiation. Contraction of erector muscles This is when the hairs on the skin are raised by the erector muscles contracting. It traps a wider layer of air between the body and the environment. Provides insulation.

22. Vasoconstriction

23. Shivering (nothing to do with the skin) • When the hypothalamus detects a drop in body temperature, nerve impulses to the skeletal muscles cause them to undergo brief repeated contractions – shivering. • This generates heat energy and helps to return the body temperature to its normal level.

24. Negative Feedback Control • Regulation of body temperature is a further example of negative feedback control. (remember water balance is too) • The mechanisms of temperature regulation of the skin are involuntary and are controlled at a subconscious level by the hypothalamus.

25. Motor nerve impulses to skin VASODILATION, INCREASED SWEATING THERMORECEPTORS IN HYPOTHALAMUS Increase in body temperature Decrease in body temperature No change in body temperature temperature remains at set point NORMAL BODY TEMPERATURE (37°C) NORMAL BODY TEMPERATURE (37°C) Decrease in body temperature Increase in body temperature THERMORECEPTORS IN HYPOTHALAMUS VASOCONSTRICTION, DECREASED SWEATING Motor nerve impulses to skin

26. No change in body temperature temperature remains at set point

27. No change in body temperature temperature remains at set point