Chapter 6: The Nervous System Sect. 1: How the Nervous System Works Sect. 2: Divisions of the Nervous System Sect. 3: The Senses

Sect. 1: How the Nervous System Works What are the functions of the Nervous System? Receive information Process information from both external (outside environment) & internal (inside the body) sources Nerve impulse: messages carried by nerve cells Respond to information Responses to stimuli can either be voluntary or involuntary. Stimulus: any change or signal in the environment that can make an organism react. Response: body’s reaction to a stimulus Maintain homeostasis Directs and coordinates the body’s response to the environment either chemically (release of hormones & other chemicals ) or mechanically (directing movement).

Neurons: nerve cells Structure of a neuron. Soma Cell body of a nerve cell Dendrite Carry impulses toward the cell body Nucleus Controls the direction of impulses Axon Carry impulses away from the cell Axon tip Connections at the end of an axon that delivers impulses to different cells Nerve: bundle of nerve fibers

Types of Neurons Sensory neurons Interneuron Motor neuron Pick up stimuli from the internal or external environment & converts it into a nerve impulse. Interneuron Connector neurons that pass nerve impulse from one neuron to another. Synapse: junction where one neuron can transfer a nerve impulse to another nerve or structure. Nerve impulses are passed across the synapse through the use of chemicals released by the axon tip. Motor neuron Neurons that carry the nerve impulse to a muscle or gland cause them to respond to the stimuli.

Sect. 2: Divisions of the Nervous System The Nervous System is divided into 2 parts…. Central Nervous System Peripheral Nervous System The Central Nervous System consists of…. Brain Spinal cord The Peripheral Nervous System consists of…. The nerves that branch out from the brain & the spinal cord.

Central Nervous System Brain Control center for most of the body’s functions. Regions of the brain Cerebrum Largest part of the brain. Controls functions such as the senses, speech, memory, movement & abstract thought. Divided into 2 half; right & left. Right half controls skeletal muscles on left side of body. Left half controls muscles on right side of body. Right half associated with creativity & artistic ability. Left half associated with logical & mathematical reasoning.

Spinal cord Cerebellum Brain stem 2nd largest part of the brain Primarily responsible for sensory integration & coordination of movement & balance. Brain stem Smallest part of the brain Responsible for controlling involuntary functions; i.e., breathing, heartbeat, etc. Spinal cord Thick column of nervous tissue that links the brain to most of the nerves of the peripheral nervous system. Protected by vertebrae, layers of connective tissue, and spinal fluid.

Peripheral Nervous System Divisions of the peripheral nervous system Somatic Nervous System Control voluntary actions Autonomic Nervous System Control involuntary actions Components Nerves that branch out from the brain & spinal cord 43 total pairs of nerves (right side body & left side body) 12 pairs extend from the brain; 31 extend from the spinal cord. Spinal nerves contain both motor & sensory neurons Sensory neurons: impulses from the body to the central nervous system Motor neurons: impulses from the central nervous system to the body

Reflex Automatic response that occurs very rapidly and without conscious control. Reflexes are controlled by spinal cord not the brain Steps to a reflex pathway Sensory neuron detect stimulus Nerve impulse travels to spinal cord Spinal cord sends return impulse to direct immediate response. Nerve impulse travels to brain where brain then interprets impulse.

Nervous System Injuries Stroke The arteries of the a part of the brain are damaged and blood flow to the area is affect. Movement (paralysis) on the opposite side of the body in which the stroke took place is usually affected Concussions bruise like injury of the brain; soft tissue of the brain collides against the skull. Symptoms of moderate to severe concussions Headaches Lose of consciousness, drowsiness Confusion Spinal cord injuries Paralysis: complete loss of muscle function for one or more muscle groups Paraplegia: loss of muscle function in the lower half of the body. Quadriplegia: loss of muscle function in all 4 limbs.

Sect. 3: The Senses What happens to light that enters the eye? Light enters through the cornea. Cornea is the clear tissue that covers the front of the eye. Light then enters the pupil. Pupil is a hole located in the center of the iris of the eye that dilates & contracts to allow more (low light areas) or less (sunny areas) into the eye. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils Iris is the colored portion of the eye that are actually muscles that control how much the pupil dilates or contracts.

Light then strikes the lens. Lens is a flexible, translucent structure that focuses the light onto the retina. Light then strikes the retina. Retina is the row of a light-sensitive tissue lining the inner surface of the back of the eye. Light striking the retina initiates a cascade of chemical and electrical events inside cells called rods & cones that ultimately trigger nerve impulses. Rods are low light receptor cells; see black, white & shades of gray Cones are high light receptor cells; see color, clarity & contrast. Image created on back of the eye is upside down & backwards.

Optic nerves connects each eye to the cerebrum. The cerebrum receives the nerve impulses from the optic nerves. It flips the image. It reverses the image. It combines the images generated from both eyes to form the single image that you see.

Common eye problems Nearsightedness Farsightedness Inability to see objects from a distance. Eyeballs tend to be elongated. Image focuses in front instead of on the retina. Corrected by the use of a concave lens that focuses the light onto the retina. Farsightedness Inability to see objects up close. Eyeballs tend to be shortened. Image focuses behind instead of on the retina. Corrected by the use of a convex lens that focuses the light onto the retina.

How do you hear? Outer Ear Middle Ear Vibrations or sound waves are created by objects in the outside environment. Those sound waves radiate or move toward your ear. You outer ear is designed to funnel those sound waves into the ear canal. Middle Ear Those vibrations travel through the ear canal and hit the eardrum causing it to vibrate. Those vibrations are then passed to the structures of the middle ear; hammer, anvil, & stirrup, causing them to vibrate.

Inner Ear The stirrup cause vibrations to pass to the structures of the inner ear, primarily the cochlea; a fluid filled, snail shaped structure that also contains sensory neurons. The sensory neurons change the vibrations into nerve impulses that are sent to the brain to be interpreted as sound.

Semicircular canals are structures within the ear that control you sense of balance. Sense of Smell Nose can distinguish between over 50 basic odors. Nasal receptors react to the smell of a food before taste receptors on the tongue. Sense of Taste Taste receptors on the tongue can determine about 5 main “tastes.” Sweet Sour Bitter Salty Umami: a “meatlike” or savory taste Taste buds change about every 7 years.

Sense of Touch Skin is the largest sense organ. Contains receptors that respond to… Light pressure Upper part of the dermis Heavy pressure Lower part of the dermis Pain Body’s early warning system for possible danger & damage to an area. Temperature Used to help regulate internal body temperature & the maintaining of homeostasis