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Nervous System

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Nervous System

master control system

master communicating center

nerve tissue develops from embryonic ectoderm

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Role of the Nervous System

monitors changes

- (sensory function) processes and interprets information

- (integrative) elicits responses

- (motor)

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Nervous System Organization

anatomical organization

- central nervous system (CNS)

- peripheral nervous system (PNS) functional organization

- sensory

- integrative

- motor

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Central Nervous System (CNS) brain

- cerebrum

- diencephalon

- brain stem

- cerebellum spinal cord

- continuation of brain stem

- continues from base of skull to the 1st lumbar vertebra

four principal parts

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cerebrum

cerebellum

pituitarygland

diencephalon

spinal cord

brain stem

midbrain

pons

medullaoblongata

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Peripheral Nervous System (PNS)

cranial nerves

- 12 pairs

- emerge from the brain spinal nerves

- 31 pairs

- emerge from the spinal cord

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Functional Organization sensory

- gathers information that occurs within internal and external environment

integrative

- analyzes sensory information

- decides necessary responses motor

- carries instructions (nerve impulses) to muscles and glands (effectors)

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Basic Types of Functional Neurons

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Sensory Neurons

afferent neurons

- carry information from various body parts to the brain or spinal cord (input)

Motor Neurons efferent neurons

- carry instructions from the CNS to muscles and glands (output)

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Interneurons or Connecting Neurons

analyze information determine appropriate response located in the CNS

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Peripheral Nervous System(subdivisions)

somatic nervous system (soma = body)

- voluntary

- sensations are consciously perceived autonomic nervous system (auto = self)

- involuntary and automatic

- sensations are usually not consciously perceived

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Somatic Nervous System(SNS)

sensory neurons

- carry impulses to the CNS from receptors for general and special senses

(touch, pressure, vibration, temperature, pain, proprioception, smell, taste, vision,hearing and equilibrium)

motor neurons

- carry impulses away from CNS only to skeletal muscles

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Autonomic Nervous System(ANS)

sensory neurons

- carry impulses to the CNS from visceral receptors (internal organs)

motor neurons

- carry impulses from CNS to smooth muscle, cardiac muscle, and glands

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Motor Division of Autonomic Nervous System

Two principal divisions work together, i.e., impulses of one division activate an organ, while impulses from the other division inhibit the organ

sympathetic parasympathetic

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Sympathetic prepares the body for energy-expending,

stressful, or emergency situations

Parasympathetic active under normal ordinary, restful

conditions counterbalances effects of sympathetic

division restores body to resting state

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Protection and Coverings of the Brain

bones of cranium cerebrospinal fluid connective tissue membranes called

meninges vertebral column

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Cranium

frontal sphenoid ethmoid occipital parietal temporal

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Cerebrospinal Fluid(CSF)

formed by filtration and secretion from networks of capillaries

- choroid plexuses

located in the (4) ventricles of the brain

form blood-brain barrier clear, colorless liquid contains glucose, proteins, lactic acid, urea,

cations, anions, and lymphocytes

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Cerebrospinal Fluid (cont.)

acts as shock-absorbing medium protects brain from banging against

inner walls of cranium is a medium for exchange of nutrients

and waste products between blood and nervous tissue

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Cerebrospinal Fluid (cont.)

significant changes in composition can indicate disease conditions

- meningitis

- tumors

- multiple sclerosis if drainage of CSF is obstructed, excessive

pressure on the brain will cause hydrocephalus

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Blood-Brain Barrier permits certain substances to enter the fluid

but prohibits others protects the brain from harmful substances formed by tightly adherent cell connections

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Meninges

protective membranes delicate envelop brain and spinal cord Three connective tissue membranes:

- dura mater

- arachnoid

- pia mater

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Dura Mater outermost layer leathery next to bony inner surface of cranium separated from arachnoid by subdural

space which is fluid filled

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Arachnoid

middle layer looks like a cobweb Two components:

- layer next to the subdural space

- system of supporting fibers (trabeculae) forming web-like structure between arachnoid and pia mater

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Arachnoid (cont.)

in some areas, arachnoid material perforates dura mater forming protrusions called arachnoid villa

Functions:

- reabsorption of CSF into blood

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Pia Mater

innermost thin layer of loose connective tissue transparent contains many blood vessels between pia mater and nerve tissue is a

thin layer of neuroglial processes firmly attached to pia mater

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Meningitis

inflammation of meninges serious threat to brain bacterial and viral meningitis can spread

to nervous tissue of CNS

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Regions of the Brain

cerebrum (cerebral hemisphere ) diencephalon brain stem cerebellum

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Cerebrum (cerebral hemisphere)

largest, obscures most of brain stem looks like mushroom cap made up of 2 deeply grooved hemispheres -

left and right Surface is covered by:

- grooves - fissures or sulci

- ridges - gyri or convolutions which serve as landmarks

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Cerebrum (con’t) concerned with higher brain functions Contains centers for:

- interpreting sensory impulses

- initiating voluntary muscular movements stores information of memory utilizes information in reasoning processes functions in determining a person’s

intelligence and personality

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Left Hemisphere

More important for:

- right-hand control

- spoken and written language

- numerical and scientific skills

- reasoning

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Right Hemisphere

More important for:

- left-hand control

- musical and artistic awareness

- space and pattern perception

- insight and imagination

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Lobes

each hemisphere is subdivided into 4 lobes

named for cranial bone that covers them

more precisely defined by surface landmarks, i.e., sulci and fissures

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Lobes (cont.)

parietal lobe occipital lobe temporal lobe frontal lobe

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White Matter

underlying the cortex whitish appearance is due to fatty

component of myelin consists of myelinated axons extending in

three principal directions

- association fibers

- commissural fibers

- projection fibers

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Association Fibers

connect and transmit impulses between gyri in the same hemispheres

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Commissural Fibers

transmit impulses from the gyri in one cerebral hemisphere to corresponding gyri in the opposite hemisphere

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Three Important Commissural Fibers

corpus callosum (corpus = mass or body)

- great commissure of the brain between the cerebral hemispheres

anterior commissure posterior commissure

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Projection Fibers

form descending and ascending tracts tracts transmit impulses from cerebrum

and other parts of brain to spinal cord tracts transmit impulses from spinal

cord to brain

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Gray Matter made primarily of densely packed neuron cell

bodies basal ganglia

- paired masses of gray matter

- found in cerebral hemispheres cerebral cortex

- layer of gray matter approx. 3 mm thick

- has 6 distinct layers

- divided into 3 areas based on function

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Cerebral Hemisphere

outer layer of gray matter is cerebral cortex

- made up of lobes composed of dendrites and cell body neurons

- interior is composed of white matter (nerve fibers arranged in bundles called tracts)

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Functions of Cerebral Cortex

divided into three main areas based on function

- sensory area

- motor area

- association area

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Sensory Areas Function in interpreting impulses,

located in several lobes of cerebrum

- general sensory area

- primary visual area

- primary auditory area

- primary gustatory area

- primary olfactory area

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Sensory Areas

general sensory

primary visual

primary gustatory

primary auditory

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General Sensory Area Receives impulses from:

- the skin

- muscles

- internal organs localizes precisely where sensations

originate located on the postcentral gryus on the

occipital lobe

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Primary Visual Area

receives input from the eyes Interprets:

- shape

- color

- movement located on the occipital lobes

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Primary Auditory Area (cont.)

receives input from internal ear (cochlea)

Interprets:

- pitch

- rhythm located on the temporal lobes

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Primary Gustatory Area

receives input from taste buds Interprets:

- sensations related to taste

(sweet, sour, salty, bitter) located at base of postcentral gryus on

parietal lobes

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Primary Olfactory Area

receives input from olfactory bulbs Interprets:

- sensations related to smell located on temporal lobes

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Motor Areas

All located on frontal lobes, control actions of specific muscles or groups of muscles

- primary motor area

- motor speech area

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Motor Areas

motor speech(Broca’s)

primary motor

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Primary Motor Area

controls muscles in specific parts of body

located on precentral gyrus of frontal lobe

The translation of thoughts into speech involves the motor speech area

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Motor Speech Area (Broca’s Area)

Coordinates complex muscular actions of the:

- mouth

- tongue

- larynx located at junction of temporal, parietal,

and occipital lobes in only one cerebral hemisphere (usually left)

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Association Areas Concerned with:

- personality

- intelligence

- emotions

- reasoning

- problem solving

- creativity judgment

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Association Areas (cont.)

somatosensory association area visual association area auditory associations area (Wernick’s

area) gnostic area premotor area frontal eye field

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Association Areas

frontal eye field

promotor somatosensory

gnostic

visual

auditory

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Somatosensory Association Area

integrates and interprets sensations Determines:

- shape and texture of an object

- orientation of one object to another as they are felt

- sense relation of one body part to another stores memories, so present sensations can

be compared to previous experiences

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Visual Association Area

relates present to past visual experiences by recognizing and evaluating what is seen

located in occipital lobe

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Auditory Associations Area (Wernick’s area)

interprets meaning of speech determines type of sound

- speech, music, and noise also interprets meaning of speech by

translating words into thoughts located inferior to primary auditory area

in temporal lobe

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Gnostic Area(gnosis = knowledge) (NOS-tik)

integrates sensory interpretations from the association areas and impulses from other areas so that a common thought can be formed

- sends signals to other parts of the brain to cause appropriate response

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Premotor Area

anterior to primary motor area neurons from this area communicate

with primary motor cortex, sensory associations areas in the parietal lobe, the basal ganglia, and the thalamus

concerned with learned motor activities of complex and sequential nature such as writing or playing the piano

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Frontal Eye Field

in frontal cortex controls voluntary scanning movements

of the eyes such as searching for a word on a page of text or dictionary

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Diencephalon

consists primarily of the thalamus and the hypothalamus

sits on top of brain stem

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Thalamus oval structure consists of paired masses of gray matter (1 inch

long) organized into nuclei form lateral walls of third ventricle right and left halves are joined by bridge of gray

matter called intermediate mass principal relay station allows crude recognition of sensations; pain,

temperature, or pressure

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Hypothalamus

under thalamus single most important region of brain for

maintaining homeostasis Regulates:

- temperature, hunger, thirst, smell, fear, rage, sexual behavior, endocrine rhythms, and posterior and anterior pituitary secretions

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Brain Stem

Three parts:

- midbrain

- pons

- medulla oblongata three inches long

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Midbrain

mesencephalon

(meso = middle, enkephalos = brain) extends from pons to diencephalon about one inch involved with visual and auditory stimuli

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Pons (pons = bridge)

directly above medulla anterior to cerebellum about one inch long consists of white matter with regions of

gray matter (nuclei) scattered throughout bridge connecting spinal cord with brain

via transverse and longitudinal fibers helps to control respiration

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Medulla Oblongata

merges with spinal cord contains all ascending and descending

tracts that connect spinal cord and various parts of brain

contains centers that control heart rate, blood pressure, breathing, swallowing and vomiting

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Cerebellum

looks like a cauliflower located behind the pons and below

occipital lobes of cerebrum controls subconscious skeletal muscle

contractions required for smooth, coordinated movements and equilibrium

“automatic pilot” second largest part of brain

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Spinal Cord

continuation of brain stem extends from large opening in base of

cranium (foramen magnum) down to upper region of the lower back (1st lumbar vertebra)

cylindrically shaped approximately 17 inches long 1 inch in diameter

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Spinal Cord (cont.)

Surrounded and protected by:

- meninges

- cerebrospinal fluid

- a layer of fatty tissue

- the vertebra no possibility of spinal cord injury below

L4; ideal site for removal of cerebral spinal fluid