The Nervous System Homework Handout

Division of the Nervous System Central Nervous System (CNS) –Consists of the brain and spinal cord –The central nervous system relays messages, processes information, and analyzes information. Peripheral Nervous System (PNS) –Consists of all the nerves outside the CNS –Senses and movement; Relays information from the external environment to the central nervous system. Somatic Nervous System Autonomic Nervous System

Peripheral Nervous System Sensory – Conveys information from sensory receptors or nerve endings Motor – Stimulates voluntary and involuntary muscles Consists of two systems –Somatic Nervous System regulates activities that are under conscious control, such as the movement of the skeletal muscles –Autonomic Nervous System Controls involuntary muscles

Autonomic System Further divided into two parts: Sympathetic –Fight-or-flight response –Increases heart and breathing rate –Liver converts glycogen to glucose –Bronchi of lungs dilate and increase gas exchange –Adrenaline raises blood glucose levels Parasympathetic –Opposes the sympathetic system –Calms the body down –Decreases heart/breathing rate –Enhances digestion

Neurons (Nerve Cells) Neuron - cell that carries messages throughout the nervous system –cell body - largest part of a typical neuron; contains the nucleus and much of the cytoplasm. –Dendrites – sensory parts of neuron. Messages are received here and transmitted to the rest of the cell by electrical impulses. (Neurons can have numerous dendrites) –Axon - long fiber that carries impulses away from the cell body of a neuron. Neurons only have one axon, but it can be several feet long. –Myelin sheath - insulating membrane surrounding the axon in some neurons. Protects and aid in transfer of electrical impulse. Formed by Schwann Cells.

Neuron

The Reflex Arc The simplest nerve response Notice that the loop is completely independent, it is not necessary to have CNS involvement beyond the relay with the interneuron.

Nerve Impulse A nerve impulse begins when a neuron is stimulated by another neuron or by its environment. resting potential - difference in electrical charge across the cell membrane of a resting neuron action potential - reversal of charges across the cell membrane of a neuron

Nerve Impulse - (Resting Potential) All living cells have a membrane potential between the cytoplasm and extracellular fluid. (-50mV to -100mV) A resting Neuron is polarized (-70mV) –Sodium-potassium pump maintains this state by pumping out + ions – Stimulus must overcome resting potential (- 70mV or possible more)

How a Neuron Functions (Resting Potential)

Nerve Impulse - Action Potential Action Potential or impulse can only be generated in the Axon. –Stimulus overcomes threshold –Membrane become more permeable Allowing Na + to rush in. Like a wave or domino affect

Nerve Impulse - Action Potential

Nerve Pulse transfer Synapse – Location where the axon terminals meet the dendrite of an adjacent neuron –Synaptic cleft is the space between Neurotransmitter - chemical used by a neuron to transmit an impulse across a synapse to another cell

Action Potential

Central Nervous System Cerebrum - area of the brain responsible for all voluntary activities of the body Cerebellum - region of the brain that coordinates body movements brain stem - structure that connects the brain and spinal cord; includes the medulla oblongata and the pons “Switchboard” Thalamus - brain structure that receives messages from the sense organs and relays the information to the proper region of the cerebrum for further processing Hypothalamus - brain structure that acts as a control center for recognition and analysis of hunger, thirst, fatigue, anger, and body temperature

Central Nervous System

The Senses of the Nervous System There are five general categories of sensory receptors: pain receptors, thermoreceptors, mechanoreceptors, chemoreceptors, and photoreceptors.

The Eye Pupil - small opening in the middle of the iris through which light enters the eye Lens - transparent object behind the iris that changes shape to help adjust the eye’s focus to see near or distant objects Retina - innermost layer of the eye Cornea – tough, clear covering that protects the eye and allows light to pass through Humor – fluids that maintain the shape of the eye Iris – colored part of the eye that controls how much light enters Rod - photoreceptor in eye that is extremely sensitive to light Cones - in the retina of the eye, a photoreceptor that responds to light of different colors, producing color vision

Eye

The Ear (Hearing and Balance) Hearing –Auditory Canal – ear canal, where sound enters –Tympanum – Ear Drum, vibrates as sound wave hit it –Cochlea - fluid-filled part of the inner ear; sends nerve impulses to the brain through the cochlear nerve –Ear bones Hammer Anvil Stirrup –Eustachian tube – equalizes pressure between environment and inner ear –Oval window – sends waves of pressure to cochlea Balance –semicircular canal - one of three structures within the inner ear that help an organism maintain balance (oriented perpendicular to each other)

Ear

Semicircular Canals

Smell and Taste Chemoreceptors – receptors which sense different Chemicals Taste and smell are linked closely together “Hold your Nose” taste bud - sense organ that detects the flavor of a substance

Touch Related Senses Touch – Mechanoreceptors Temperature – Thermoreceptors Pain – Pain Receptors

Questions 1.Name the five types of sensory receptors and list where they are found in the body. 2.Identify the parts of the eye and the function of each part. 3.What parts of the ear are responsible for hearing? For balance? 4.Explain why you can’t “taste” food when you have a bad cold. 5.Why do you feel dizzy after spinning around? How can a dancer or ice skater do lengthy spins?