The Human Nervous System and The Human Endocrine System Dr. Rose

Divisions of the Nervous System The human nervous system is divided into central and peripheral components. 1. Central Nervous System (CNS) consists of the brain and the spinal cord. 2. Peripheral Nervous System (PNS) consists of nerves outside the CNS.

The Neuron The cells that carry messages throughout the nervous system are called neurons. Whatever their specific function, all neurons have the same physical parts: The cell body, dendrites and the axon.

Neuron Structure A neuron consists of 3 main parts: Cell Body - contains the nucleus Dendrites - short branch extensions spreading out from the cell body. These receive the impulse. Axon – a long fibre that carries impulses away from the cell body. The axons of most neurons are covered with a lipid layer known as the myelin sheath which acts as an insulating material.

Neuron Types Neurons can be classified into 3 main types: 1. Sensory neurons carry impulses from the sense organs/receptors to the CNS. 2. Relay (Inter) neurons carry impulses from neuron to neuron within the CNS. 3. Motor neurons carry impulses from CNS to muscles and glands/effectors.

Reflex Arcs Neurons are linked in functional pathways called reflex arcs. A reflex action is an automatic response which you cannot control. Reflex arcs can be illustrated by using the Stimulus-Response Model.

Stimulus-Response Model Something in the environment which causes a behaviour response is a stimulus. The receptor (sense organ) detects the stimulus, a message is sent to the effector (muscle/gland which responds to nerve impulse) which brings about a response. The entire nervous system provides a system of interconnecting links between receptors and effectors.

The Synapse Neurons that transmit impulses to other neurons do not touch one another. The small gap between the axon of one neuron and the dendrites on the next neuron is called the synapse. The synapse ensures one-way transmission of impulses. A nerve impulse cannot go backwards across a synapse.

Transmission of Nerve Impulses Messages move down the axon as electrical impulses The movement of sodium (Na+) and potassium (K+) causes the impulse Once it gets to the synapse it stops Chemical messengers called Neurotransmitters then pass the message through the gap to the dendrites of the next neuron

The Human Brain The human brain consists of two types of tissue: White matter is tissue made of axons. Grey matter is tissue made of cell bodies. There are 3 main divisions to the human brain: The Cerebrum, Cerebellum and Brainstem

The Cerebellum Coordinates movement. Responsible for balance and performing some cognitive abilities such as those involved in speech and language. Also involved in hand – eye co-ordination

The Brainstem The most primitive part of the brain Controls vital, reflexive functions such as breathing, blood pressure Also swallowing, vomiting and digestion

Diencephalon Thalamus: Link between the cerebrum and the rest of the brain Hypothalamus and Pituitary: Makes hormones and links the nervous system to the endocrine system

The Cerebrum Made up of two parts- left and right hemispheres. Responsible for cognitive processes such as learning, memory and thinking. Can be divided into 4 lobes: Frontal- thought,speech, movement, motivation, foresight, emotions and feelings Parietal- touch, taste, some speech Occipital- sight, visual recognition Temporal- auditory and smell

Nervous control Hormonal control Communication Impulses across synapses Hormones in the blood Speed Very rapid (ms) Relatively slow (min – hour or longer) Duration Short term & reversible Longer lasting Target pathways Specific (through nerves) to specific cells Hormones broadcast to target cells everywhere Action Causes glands to secrete or muscles to contract Causes changes in metabolic activity

The Human Endocrine System The endocrine system consists of glands which release hormones. Endocrine glands are ductless- they don’t release their product into a duct as exocrine glands (salivary, sweat) do. Instead endocrine glands secrete hormones into the blood which transports them around the body.

The Human Endocrine System As the hormones pass cells, only those with special receptors will react to the presence of the hormone. These are called target cells.

Pituitary gland

Pituitary gland Known as the master gland because it secretes a number of hormones which influence other endocrine organs. Makes human growth hormone.

Thyroid gland

Thyroid gland Secretes thyroxine which controls metabolic rate and is important in regulation of body temperature. Iodine is important for the thyroid tissue. Goiter results from lack of iodine.

Adrenal glands

Adrenal glands Secrete adrenaline which is called the fight or flight hormone because it prepares the body for action. More glycogen is converted to glucose Faster heartbeat The above all help to provide more glucose and more oxygen for working muscles.

Pancreas

Pancreas Regulates sugar balance Secretes two hormones: insulin and glucagon Insulin lowers blood sugar and stores it as glycogen. Glucagon increases blood sugar by stimulating glycogen breakdown.

Negative Feedback Blood glucose concentration is regulated by negative feedback. High blood sugar Low blood sugar Pancreas makes insulin Pancreas makes glucagon Sugar enters cells Glucose to glycogen Sugar leaves liver Glycogen to glucose Blood sugar level lowered Blood sugar is increased

Diabetes Diabetes is a condition where there are higher than normal blood glucose levels. Usually the result of the failure of the pancreas to secrete enough insulin. Treatment is by regular injection of pure insulin- much of this is now manufactured by genetic engineering.