Animal Physiology

Animal Physiology The Brain & Nervous System Mr G Davidson

Structure of the Brain • The brain is made up of several different parts. • Each part has its own specialised function. • The main part of the brain, the cerebrum, is divided into 2 parts called the cerebral hemispheres, which are connected together. G Davidson

Cerebrum Cerebellum Medulla Structure of the Brain G Davidson

Structure of the Brain G Davidson

Structure of the Brain • The cerebrum collects information from the sense organs in the sensory area in the left hemisphere. • It then sorts out this information. • It can now respond by sending out signals from the motor area to the appropriate muscles. G Davidson

Sensory Area Motor Area Structure of the Brain G Davidson

Nervous System • The nervous system is made up of three parts: • Brain • Spinal cord • Nerves • The brain and the spinal cord together make up the Central Nervous System. G Davidson

Nervous System • The brain is protected inside the skull and the spinal cord is protected inside the vertebrae of the spine. • The nervous system consists of nerve cells called neurones. • Impulses are brought to the brain by the sensory nerves. • Impulses leave the brain in the motor nerves. G Davidson

Nervous System • A sensory neurone has a sensory fibre which carries the impulse from a receptor towards the cell body. • The axon fibre carries the impulse from the cell body towards the Central Nervous System. • Some sensory neurones can be very long (up to 1m). G Davidson

Cell body Direction of flow of impulse Impulse to CNS Receptor Sensory fibre Axon fibre Sensory Neurone G Davidson

Nervous System • Motor neurones have a cell body containing a nucleus at the start of the neurone. • Attached to this is the long axon fibre. • At the other end are the motor end plates which attach to a muscle or gland. G Davidson

Cell body Direction of nerve impulse Impulses from the CNS Axon fibre Effector (muscle/gland) Motor Neurone G Davidson

Nervous System • There is a third type of neurone called a relay neurone. • These are found within the CNS. • There job is to relay impulses from the sensory nerves to the motor nerves as quickly as possible so the body can respond with a reflex action. G Davidson

Direction of impulse Impulses from sensory neurones Impulses to other neurones Cell body Main relay fibre Relay Neurone G Davidson

Reflex Action • A reflex action is a rapid response by the nervous system without the brain processing it. • A reflex arc is an arrangement of 3 neurones: • Sensory neurone • Relay neurone • Motor neurone G Davidson

Reflex Action • Information travels along the sensory nerve and passes across a small gap called a synapse, into the relay nerve in the spinal column, and from here straight into the motor nerve and back to the muscles. • This offers some degree of protection to the body. G Davidson

Reflex Action G Davidson

Reflex Actions G Davidson

Control of Body Temperature • The nervous system is also responsible for controlling the body’s internal environment. • The hypothalamus contains thermoreceptors which detect changes in the temperature of the blood. G Davidson

Control of Body Temperature • It responds by sending out nerve impulses mainly to the skin to try to return the body temperature to normal. • Since the skin is in immediate contact with the external environment it plays a major role in temperature regulation. G Davidson

Correction of overheating • If the body temperature increases the skin can take the following actions to try to bring the temperature back down. • Increase the rate of sweating. Heat energy from the body is used to evaporate the sweat. • Relaxation of hair erector muscles. This prevents heat being trapped in a layer of air next to the skin and allows it to escape. • Vasodilation. Arterioles near the surface of the skin dilate allowing more blood to the surface where it can lose heat by radiation. G Davidson

Much Heat Lost by Radiation Environment skin Arteriole becomes dilated Shunt vessel narrows Nerve impulses from hypothalamus Vasodilation G Davidson

Correction of Overcooling • If the body temperature decreases the skin can take the following actions to try to bring the temperature back up. • Contraction of hair erector muscles. This traps a layer of warm air at the skin which acts as extra insulation. • Decreased rate of sweating. Little or no energy is lost trying to evaporate sweat. • Vasoconstriction. Arterioles near the surface of the skin constrict allowing less blood to the surface and therefore less heat is lost by radiation. G Davidson

Little Heat Lost Environment skin Arteriole becomes constricted Shunt vessel dilates Nerve impulses from hypothalamus Vasoconstriction G Davidson

Other Responses to Temperature Changes • Shivering. Nerve impulses are sent by the hypothalamus to the skeletal muscles to bring about shivering, which generates heat energy. This helps raise the body temperature. • Increase in metabolic rate. The liver produces extra heat in order to raise the temperature of the body. G Davidson

Negative Feedback Control • Negative feedback control brings about changes which help return the body to normal conditions. • If the body temperature drops, negative feedback control raises the temperature, and vice versa for the body temperature being raised. G Davidson

Thermoreceptors Increased sweating, vasodilation Decrease in body temperature Increase in body temperature No Change Normal body temperature (37oC) Normal body temperature (37oC) Decrease in body temperature Increase in body temperature Thermoreceptors Shivering, vasoconstriction Temperature Regulation G Davidson

Temperature Regulation • All of the methods to regulate body temperature mentioned so far, are involuntary responses. • There are, of course, voluntary responses which we can use to regulate our body temperature. G Davidson

Temperature Regulation • These include: • When it is hot • Removing clothes • Taking a long cold drink • Finding a cooler place • When it is cold • Putting on extra clothes • Turn up the heating • Hot drinks G Davidson

Animal Physiology