Nervous System

10-1 An Overview of the Nervous System

•  The nervous system controls body functions.

•  It also allows for higher functions such as thinking.

The Central Nervous System •  The nervous system consists of two parts: the central and

peripheral nervous systems.

–  The central nervous system (CNS) is made up of the brain and spinal cord.

–  Receptors transmit sensory input to the CNS via sensory neurons.

–  The CNS integrates all sensory input and generates appropriate responses.

–  Motor output leaves the CNS in motor neurons.

The Peripheral Nervous System

•  The peripheral nervous system (PNS) consists of: – spinal nerves – cranial nerves

•  The peripheral contains the somatic and the autonomic subdivisions. – The autonomic division controls involuntary

actions. – The somatic division largely controls voluntary

actions.

What you should know now

•  CNS (Central Nervous System) –  Brain –  Spinal Cord

•  PNS –  Cranial Nerves –  Spinal Nerves –  Somatic

•  Deliberately controlled cause action of skeletal muscles

–  Autonomic •  involuntary movements cause action in Smooth

and Cardiac muscle

10-2 Structure and Function of the Neuron •  The fundamental unit of the nervous system is the

neuron.

•  This highly specialized cell generates and transmits bioelectric impulses.

The Structure of the Neuron

•  All neurons consist of a cell body and two types of processes. – Dendrites: conduct impulses to the cell body. – Axons: conduct impulses away from the cell body. – The terminal ends of axons branch, forming fibers

that end in small knobs called terminal boutons.

The Myelin Sheath

•  Axons in the CNS and PNS contain an insulating layer, the myelin sheath.

•  It greatly increases the rate of transmission of nerve impulses.

•  Nerve impulses “jump” over gaps in the sheath, the nodes of Ranvier.

Nerve Cell Repair

•  Neurons lose the ability to divide.

•  Neurons that die cannot be replaced by existing cells.

•  Undamaged, live neurons can sometimes take over the function of those that are damaged or die.

Oxygen Sensitivity of Nerve Cells

•  Neurons have a high metabolic demand.

•  They are highly susceptible to loss of oxygen and glucose.

•  Lack of oxygen in the brain often results in permanent brain damage.

•  The longer the oxygen deprivation, the greater the damage.

Build a nerve cell

•  Get some pipe cleaners and build a neuron –  Include

•  Axon •  Dendrites •  Cell body •  Terminal boutons •  Is yours myelinated or nonmyelinated

What you should know now

•  Structure of a Nerve – Cell Body – Dendrites – Axon – Myelinated Nerves – Nonmyelinated nerves

•  Nerve Cells are special – The can not divide so nerve tissue does not

repair

Nerve Cell Impulses

•  Nerve impulses result from the flow of ions across their plasma membranes.

•  The electrical potential across the membrane is known as the membrane potential or resting potential.

The Action Potential •  When a nerve cell is stimulated, its plasma

membrane increases its permeability to sodium ions.

•  Sodium ions rush in, causing depolarization down the membrane.

•  Depolarization is followed by repolarization.

•  The depolarization and repolarization of the neuron’s plasma membrane constitute a bioelectric impulse or action potential.

All or nothing: If the influx of Na+ is not enough to reach the +30 mark (action potential) then no signal will be propagated

McGraw Hill Nerve Impulse

Nerve Cell Transmission

•  Nerve impulses are waves of depolarization.

•  Depolarization in one region increases membrane permeability in adjacent regions.

•  This causes depolarization of the new region.

A relay of Neurons: Synaptic Transmission

•  Nerve impulses travel from one neuron to another across synapses.

•  When an impulse reaches the terminal bouton, it stimulates the release of neurotransmitters.

Excitation and Inhibition

•  Neurotransmitters may excite or inhibit the postsynaptic membrane.

•  If the number of excitatory impulses exceeds the number of inhibitory impulses, a nerve impulse will be generated.

Limiting a Neuronal Response

•  Neurotransmitters are quickly removed from the synapse.

•  They are destroyed by enzymes in the synaptic cleft.

Altering Synaptic Transmission

•  Many common chemical substances alter synaptic transmission.

–  Insecticides – Anesthetics – Antidepressants – Caffeine – Cocaine

Serotonin

•  Prozac : A Serotonin reuptake inhibitor relieves the symptoms of depression by altering the levels of Serotonin at neural synapses

What you should know now

•  Function of a Nerve – What is an action potential – What ions are involved in transmitting the

action potential – What is depolarization and repolarization

•  How are nerve signals propagated from one neuron to another? – Synapses – Neurotransmitter

10-3 The Spinal Cord and Nerves

•  The spinal cord is part of the central nervous system

Spinal Nerves •  The spinal cord gives off numerous nerves

that supply the body. •  The central portion of the spinal cord is an H-

shaped zone of gray matter. –  It contains nerve cell bodies

•  The white matter contains axons and dendrites.

Efferent versus Afferent

•  Afferent nerves carry information to the central nervous system – SENSORY NEURONS

•  Efferent nerves carry information from the central nervous system to the body – MOTOR NEURONS

Interneurons: Hub between Afferent and Efferent

•  Interneurons connect sensory( AFFERENT) and motor neurons(EFFERENT) in the spinal cord.

•  In the reflex arc, sensory impulses from receptors reach effectors without traveling to the brain. – Some reflex arcs do not contain interneurons. – Think about how a reflex is different from a

deliberate movement of your muscles

Damage to the Spinal Cord

•  Injury to the spinal cord can cause permanent damage. – Take a second and think about neurons and

why damage to them can lead to long term effects

•  The severity of the injury depends on: –  its location –  the extent of the damage

What if you could replace neural cells?

What you should know now

•  Structure of the spinal cord – One main cord of gray matter with axons and

dendrites extending out from the cord

•  Afferent from the body to the CNS – Sensory

•  Efferent from the CNS to the body – Motor

•  Interneurons •  Connect the afferent and efferent

•  Reflex arc •  May not have interneurons •  Evolved for quick response to dangerous

situations

•  Damage to the Spinal Cord can lead to paralysis •  One treatment utilizes stem cells

10-4 The Brain •  The brain is part of the central nervous system.

•  Cranial nerves are attached to the brain. –  They supply structures in the head and upper body.

The Cerebrum

•  The cerebral hemispheres function in integration, sensory reception, and motor action.

– The cerebrum with its two cerebral hemispheres is the largest part of the brain.

– The outer layer of each hemisphere is the cortex.

– The cerebral cortex consists of many discrete functional regions including motor, sensory, and association areas.

The Primary Motor Cortex

•  The primary motor cortex controls voluntary movement.

•  Each region of the motor cortex controls a specific body part.

•  A conscious thought stimulates the neurons of the primary motor cortex to generate an impulse.

The Primary Sensory Cortex and The Association Cortex

•  The primary sensory cortex receives sensory information from the body.

•  The association cortex is the site of integration and complex intellectual activities.

Unconscious Functions

•  Unconscious functions are housed in the: – Cerebellum – Hypothalamus – Brain stem

The Cerebellum

•  The cerebellum: – controls muscle synergy – helps maintain posture

•  Cerebral palsy is the result of severe impairment of the cerebellum. – This can be caused by lack of oxygen.

The Thalamus and Hypothalamus

•  The thalamus is a relay center. –  It relays some sensory information to the sensory

and association cortexes. •  The hypothalamus controls many autonomic

functions involved in homeostasis. – Appetite – Body temperature – Water balance – Blood pressure

The Limbic System

•  The limbic system is the site of instinctive behavior and emotion.

•  Stimulation of specific regions within the limbic system may elicit sensations.

What you should know now about the brain

•  Cranial Nerves – Control senses and movement of head and

face •  Cerebrum

– Contains 2 hemispheres –  integration, sensory reception, and motor

action. •  Cerebral Cortex : outer layer ( gray matter)

– has many discrete areas that carry out sensory , motor, integration

Involuntary centers – Cerebrum

•  Controls muscle synergy (smooth movements ) •  Maintains body posture •  Cerebral palsy is caused by damage to cerebrum

and leads to jerky body movements and inability to control motion

– Thalamus and Hypothalamus •  Controls autonomic functions and triggers the

release of hormones – The limbic system

•  Insticts •  Emotions

Cerebrospinal Fluid

•  Cerebrospinal fluid cushions the CNS.

•  It is similar in composition to blood plasma and interstitial fluid.

•  Hydrocephalus occurs in children when CSF does not drain properly into the bloodstream.

Measuring Electrical Activity of the Brain

•  Electrical activity of the brain varies depending on activity level or level of sleep.

•  Electrodes applied to different parts of the scalp detect electrical activity in the brain. – This produces an electroencephalogram (EEG).

•  EEGs are used to diagnose brain dysfunction.

10-6 Learning and Memory •  Learning is the acquisition of new information

and skills.

•  Memory is the storage and recall of information.

•  Short-term memory retains information for periods of seconds to hours.

•  Long-term memory holds information for periods of days to years.

Where are Memories Stored?

•  Memory is stored in multiple regions of the brain: – Temporal Lobe – Cerebellum – Limbic System

•  The hippocampus appears essential for transferring short-term memories into long-term memory.

How are Memories Stored?

•  Short-term and long-term memory may involve structural and functional changes in neurons.

•  Short-term memory may involve temporary changes in the function of synapses.

•  Long-term memory may involve permanent structural and functional changes.

Maintaining Mental Acuity in Old Age

•  New evidence suggests that brain function can be retained in old age.

•  Connections among brain cells may strengthen over time if individuals remain intellectually challenged.

•  Regular aerobic helps elderly people perform certain mental functions.

10-7 Diseases of the Brain Alzheimer’s Disease

•  Alzheimer’s disease is a progressive loss of mental function.

•  The brains of Alzheimer’s patients contains fibrous clumps of protein from degenerated nerve cells.

•  Proteins called beta-amyloid may bind to nerve cells in the brain and cause cell death.

Parkinson’s Disease

•  Parkinson’s Disease is characterized by: – Tremors – A lack of dopamine in the brain

•  It is caused by progressive deterioration of brain centers that control movement.

•  Drugs and surgery can be used in treatment.

Multiple Sclerosis (MS)

•  MS is caused by a destruction of the myelin sheath of nerve cells in the CNS.

•  The damaged myelin results in nerve cell death that leads to: – numbness – slurred speech – paralysis

Brain Tumors •  Two types of tumors develop in the brain tissue:

–  benign –  malignant

•  Benign tumors do not grow uncontrollably or spread. –  They can cause problems by placing pressure on areas of the brain.

•  Malignant tumors grow rapidly. –  They may place pressure on or invade adjacent tissue or other parts of

the body.

•  Brain tumors may be related to: –  Exposure to certain materials or chemicals –  Heredity –  Certain viruses

What you should know now

•  Detecting disease of the CNS – Cerebrospinal fluid

•  It is similar to plasma and bathes the CNS •  It can be examined for signs of infection

– Electroencephalogram •  Measures brain activity

•  Learning and Memory – 2 types of memory

•  Short term –  Temporary changes to neural structure

•  Long term –  Permanent changes to neural structure

•  Diseases of the brain – Alzheimer’s

•  Protein plaque build up destroys neurons

– Parkinson’s •  Tremors caused by lack of dopamine and damage

to centers that control movement – Multiple sclerosis

•  Damage to schwann cells (sheath) •  Numbness, speech problems, paralysis

– Brain Tumors •  Benign •  Malignant

Chapter 11

The Senses

11-1 The General and Special Senses •  The body contains two types of senses:

general and special.

•  Receptors for the senses are grouped into five functional categories: – Mechanoreceptors – Chemoreceptors – Thermoreceptors – Photoreceptors – Nociceptors

11-2 The General Senses

•  Receptors for the general body senses generally fit into two groups: – Naked nerve endings – Encapsulated receptors

•  Naked nerve endings in body tissues detect – Pain – Temperature – Light touch

Encapsulated Receptors

•  Encapsulated receptors are naked nerve endings surrounded by one or more layers of cells. – Encapsulated receptors detect:

•  pressure •  light touch •  muscle extension

•  Receptors play an important role in homeostasis.

Adaptation

•  Many receptors stop generating impulses after exposure to a stimulus for some length of time.

•  Muscle stretch receptors and joint proprioceptors do not adapt.

11-3 Taste and Smell

•  The special senses include – Taste – Smell – Vision – Hearing – Balance

Taste Buds

•  Taste buds respond to chemicals dissolved in food.

– They are located principally on the upper surface of the tongue.

– Food molecules dissolve in the saliva. •  They bind to the membranes of the microvilli of the

receptor cells.

Primary Flavors

– Taste buds respond to five flavors: •  Salty •  Bitter •  Sweet •  Sour •  Umami

– Taste buds are preferentially responsive to one flavor.

The Olfactory Epithelium

•  The olfactory epithelium is a patch of receptor cells that detects odors.

–  It is located in the roof of the nasal cavities.

–  The receptor cells respond to thousands of different molecules.

–  The molecules bind to membrane receptors on the olfactory hairs.

•  This stimulates nerve impulses that are transmitted to the brain via the olfactory nerve.

•  Smell influences our sense of taste, and vice versa.

11-4 The Visual Sense: The Eye •  Human eyes are roughly spherical organs located

in the eye sockets, or orbits.

•  The eye is attached to the orbit by six small muscles that control eye movement.

Anatomy of the Eye

•  The human eye consists of three distinct layers.

•  The outermost layer consists of: –  the sclera –  the cornea

•  The middle layer consists of: –  the choroid –  the ciliary body –  the iris

•  The innermost layer is the retina (the light-sensitive layer). – The retina contains two types of photoreceptors:

•  Rods: –  function in dim light –  provide black-and-white vision

•  Cones –  Cones operate in bright light and provide color vision. –  Cones are also responsible for visual acuity.

•  A very small number of the ganglion cells are also sensitive to light.

•  The cornea and lens focus light on the retina.

•  The shape of the lens is controlled by the muscles in the ciliary body. – The curvature of the lens adjusts to focus on

items.

•  The cornea cannot adjust for focus. Figure 11-8

Focusing Light on the Retina

Visual Problems •  Nearsightedness results when the eyeball is slightly

elongated.

•  Farsightedness results when the eyeballs are too short or the lens is too weak

•  Astigmatism occurs when the cornea and lens are slightly disfigured.

•  Laser surgery can correct visual defects.

•  Presbyopia is caused by a decline in the resiliency of the lens.

•  Color Blindness is a hereditary disorder that varies in severity.

Laser Surgery

Laser Surgery

Laser Surgery

11-5 Hearing and Balance: The Cochlea and Middle Ear

•  The ear consists of three anatomically separate portions: –  the outer ear –  the middle ear –  the inner ear

The Anatomy of the Ear

•  The outer ear consists of the auricle and external auditory canal. – Both direct sound to the eardrum.

•  The middle ear consists of the eardrum and three small bones, the ossicles. – The ossicles transmit vibrations to the inner ear.

•  The auditory tube equilibrates the pressure inside the middle ear cavity.

The Eustachian Tube

•  The Eustachian tube helps to equalize pressure in the middle ear.

•  The inner ear contains the cochlea, where the receptors for sound are located.

Structure and Function of the Cochlea •  Hearing requires the participation of several

structures.

–  The cochlea is a spiral-shaped, bony structure. •  It contains three fluid-filled canals.

–  The flexible basilar membrane that supports the organ of Corti separates the middle canal from the lower canal .

•  Hair cells in the organ of Corti are embedded in the relatively rigid tectorial membrane.

–  Sound waves create vibrations in the eardrum and ossicles, which are transmitted to fluid in the cochlea.

•  Pressure waves in the cochlea cause the basilar membrane to vibrate. – This stimulates the hair cells.

•  Pressure waves resulting from a sound cause one part of the membrane to vibrate maximally.

•  The hair cells stimulated in that region send signals to the brain. – The brain interprets signals as a specific pitch.

Distinguishing Pitch and Intensity

Hearing Loss

•  Conduction deafness occurs when the conduction of sound waves to the inner ear is impaired. –  It may result from a rupture of the eardrum or

damage to the ossicles.

•  Nerve deafness results from physical damage to: –  the hair cells –  the vestibulocochlear nerve –  the auditory cortex

The Vestibular Apparatus •  The vestibular apparatus houses receptors that

detect body position and movement. –  It contains:

•  semicircular canals •  utricle •  Saccule

–  Fluid movement inside the semicircular canals deflects the cupula lying over the receptor cells.

•  This alerts the brain to head movements.

–  The utricle and saccule contain receptors that respond to: •  linear acceleration •  tilting of the head

11-6 Health and Homeostasis

•  Many general sense receptors play an important role in homeostasis.

•  Noise pollution in our environment affects homeostasis by: – disturbing sleep –  raising stress levels