Biology

The Nervous System Two main parts: –Central Nervous System Consists of the brain and spinal cord –Peripheral Nervous System Consists of nerve cells that send messages between the central nervous system and all the parts of the body

Neurons Neurons- nerve cells –Send and receive messages from other structures in the body such as muscles and glands

Neurons Components of a neuron –Cell Body- produces energy that fuels the activity of the cell –Dendrites- thin fibers which branch out of the cell, receive information from other neurons and pass the message through the cell body –Axon- carries messages away from the neuron, single fiber –Myelin- covering of the axon, insulates and protects the axon, helps to speed up the transmission of the message –Axon terminal- small fibers branching out from an axon

Types of Neurons Sensory- carry messages from sense organs to spinal cord or brain Motor- carry messages from spinal cord or brain to muscles or glands Interneurons- carry messages from one neuron to another and do most of the work of the nervous system

How do Neurons communicate? Neurons send messages across synapses through the release of neurotransmitters –Chemicals that are stored in sacs in the axon terminal

Nerve Impulses Absolute refractory period- after one cell firing, it will not fire again regardless of how strong the incoming message is Relative refractory period- time when neuron is returning to normal and may refire if message is stronger then usual All or none law- a neuron fires at full capacity or does not fire at all

Firing of a nerve cell Dendrite or cell body picks up message If message is strong enough, neuron fires and impulse starts down the axon Out the end of the axon terminal to the synaptic knob On to the next nerve cell

Central Nervous System 2 major parts –Central Nervous System- brain and spinal cord –Peripheral Nervous System- connects brain, spinal cord to every other part of the body

Brain Areas of the Brain –Hindbrain- co-ordinate motor activity, posture, equilibrium, sleep patterns, and regulate unconscious functions (ex. blood circulation and breathing) –Midbrain- vision, hearing, motor control, sleep/awake cycle, arousal (alertness), and temperature regulation –Forebrain- controls cognitive, sensory, and motor functions, regulate body temperature, reproductive functions, eating, sleeping, and display of emotions

Brain Parts of the Brain –Amygdala- storing & classifying emotional memories, produces emotions –Hippocampus- memory formation, classifying information, long-term memory –Thalamus- sensory signals, visual information, information from skin and internal organs, motor control –Hypothalamus- metabolic processes, body temperature, hunger, thirst, fatigue, anger, and circadian cycles

Brain –Cerebellum- regulates & coordinates movement, posture, and balance –Pons- relays messages to other parts of the brain, controls arousal, and respiration –Medulla Oblongata- heart rate, respiration, blood pressure, swallowing, vomiting, and defecation, relay station for nerve signals going to/from the brain

Brain Lobes of the Brain –Occipital- receives and interprets visual information –Temporal- controls hearing and some processing of visual and olfactory information –Parietal- responds to sensations of touch bodily position –Frontal- responsible for voluntary movement- attention, goal-directed behavior, and appropriate emotional experiences

Brain Hemispheres –Left- right-hand touch and movement, speech, language, and writing –Right- left-hand touch and movement, spatial construction, non-verbal imagery, and face recognition

Peripheral Nervous System Carries messages to and from the Central Nervous System Made of two major parts –Somatic Nervous System –Autonomic Nervous System

Somatic Nervous System Composed of all sensory (afferent) neurons that carry information to the CNS and all the motor (efferent) neurons that carry messages from the CNS to the skeletal muscles of the body The senses have their origin in the somatic part of the Peripheral Nervous System

Autonomic Nervous System Composed of all the neurons that carry messages between the CNS and all the internal organs of the body (glands and smooth muscles such as the heart and digestive system) Important in breathing, blood flow, and emotions Has two branches- sympathetic and parasympathetic –Both are involved in controlling and integrating actions of the glands and smooth muscles

Sympathetic and Parasympathetic Nervous Systems Sympathetic –Tell the body to prepare for an emergency Heart pounds, breathe faster, pupils enlarge, & digestion stops Tells the endocrine system to release chemicals into bloodstream Connect to every internal organ of body Parasympathetic –Calms the body down after stress

The Endocrine System Consists of glands which secrete hormones into the bloodstream –Hormones- stimulate growth and affect behavior and emotional reactions produced by different glands- pituitary, thyroid, adrenal, testes, and ovaries

Pituitary Gland Lies below the hypothalamus Considered the “Master Gland” Secretes different hormones –Growth- regulates growth of muscles, bones, and glands –Prolactin- stimulates production of milk in nursing women –Oxytocin- stimulates labor in pregnant women

Thyroid Gland Produces thyroxin –Affects the body’s metabolism- the rate of converting food to energy –Low production can lead to hypothyroidism- can cause people to be overweight –High production can lead to hyperthyroidism- can cause excitability, inability to sleep, and weight loss

Adrenal Gland Located above the kidneys Secretes cortical steroids- increase the resistance to stress and promote muscle development, can cause the liver to release stored sugar in emergencies Produce adrenaline and noradrenaline –Arouse the body for an emergency –Adrenaline- can intensify emotions (fear & anxiety) –Noradrenaline- raises blood pressure

Testes and Ovaries Testes- males Ovaries- females Each produces hormones- testosterone, estrogen, and progesterone

Testosterone Testosterone- male sex hormone, small amount found in females Influences the development of sex organs (if secreted child will be male, if not- female) Aids in growth of muscle and bone, primary and secondary sex characteristics –Primary sex characteristics- directly involved in reproduction –Secondary sex characteristics- distinguish males from females

Estrogen & Progesterone Female sex hormones but small amounts are found in males Females- ovaries produce estrogen and progesterone Males- testes produce estrogen and progesterone

Estrogen & Progesterone Estrogen-Development of primary and secondary sex characteristics Progesterone- stimulates growth of female reproductive organs and prepares the body for pregnancy Both regulate menstrual cycle and vary during the cycle –Changing levels of estrogen are linked to PMS –Estrogen is connected to cognitive functioning and feelings of well-being among women