Is further divided into: Sympathetic – regulates actions during stressful situations Parasympathetic – regulates actions during nonstressful situations

NERVOUS SYSTEM

The master controlling and communicating system of the body --- cells communicate via electrical and chemical signals. Signals are rapid, specific and cause almost immediate responses. Functions include: 1. Sensory Input – sensory receptors monitor changes

occurring inside and outside the body 2. Integration – process & interprets sensory input and

makes decisions about what to do 3. Motor Output – response that activates muscles or

glands (effector organs)

Organization of Nervous System – 2 subdivisions: Central Nervous (CNS) – consist of the brain and spinal cord. The function is integration Peripheral Nervous (PNS) – consist of nerves extending from the brain and spinal cord to the

body. The functions are sensory input and motor output. The PNS is further divided into:

Nervous Tissue – neuroglia & neurons NEUROGLIA cells – insulate, support & protect; cells are unable to transmit impulses and never lose the ability to mitotically divide

Schwann cells – cells form the myelin sheaths of neurons in PNS NEURONS – cells that conduct impulses; exhibit extreme longevity can live 100 years or more. They are amitotic (can’t divide) and have a high metabolic rate – require continuous supply of oxygen and glucose.

Neuron Anatomy – Dendrite: slender fiber extensions containing sensory receptors that conduct impulse toward soma Axon: single fiber extension that generate nerve impulses and conducts impulses away from soma. Axon terminal: end branches of axon terminal branches that contain neurotransmitter storage vesicles Myelin: white, fatty material that protects and insulates fibers; speeds up impulse transmission. Nodes of Ranvier: gaps between myelin sheaths Synapse: junction of two neurons; space at synapse is called synaptic cleft

Afferent or Sensory Division

Efferent or Motor Division

Fibers transmit impulses from the body to the CNS

Somatic (SNS) - Fibers send impulses from CNS to control voluntary action of skeletal muscle

Autonomic (ANS) - Fibers send impulses from CNS to regulate involuntary actions of smooth muscle, cardiac muscle & glands

Sensory receptors on dendrites receive impulse.

Impulse is sent to cell body, then through the axon jumping from node to node.

When impulse reaches terminals, a neurotransmitter is released to stimulate the receptors on dendrites of another neuron.

Neuron Physiology

1. Plasma membrane of a resting (inactive) neuron is polarized, which means the outside of cell is more positive than the inside. All gated Na+ and K+ channels are closed – this maintains the resting membrane potential.

2. Stimulus changes permeability of membrane and Na+ diffuse into cell to change polarity – this is depolarization. For axon to “fire”, depolarization must meet threshold causing action potential.

3. Action potential travels down the axon as opened Na+ gates stimulate neighboring Na+ gates to open.

4. Action potential is created – impulse travels through neuron jumping from node to node.

5. In response to the inflow of Na+, K+ channels open. K+ diffuses out of the cell to restores the electrical conditions – this is called repolarization. Soon after the K+ gates open, the Na+ gates close. Repolarization must occur to conduct another impulse.

6. Na/K pump uses ATP to restore the initial concentrations of Na & K to resting ionic conditions – refractory period.

7. These events continue to spread across the membrane of the neuron until the impulse reaches the axon terminal.

8. At axon terminal, impulse triggers vesicles to release neurotransmitters

9. Neurotransmitters bind to receptors on dendrite of next neuron – process occurs again on next neuron.

Cell Death - about 2/3 of neurons die before birth if they do not form synapse with target cells; many cells also die due to apoptosis (programmed cell death) during development

Multiple Sclerosis (MS) – autoimmune disease in which immune system attacks myelin. Impulse conduction is slow and eventually ceases.

Central Nervous System (CNS)

BRAIN – 4 parts

Cerebrum Nearly the entire surface of the cerebral hemispheres has elevated ridges of tissue called gyri which are separated by hallow grooves called sulci. Deeper grooves are called fissures --- these grooves separate larger regions of the brain. The cerebrum has 2 hemispheres and 4 lobes.

Cerebral cortex - outermost area consists of GRAY MATTER (unmyelinated fibers) – integration occurs here! o Each hemisphere is concerned with the contralateral (opposite) side of the body. o No functional areas of the cortex work alone -- conscious behavior involves entire cortex in some

way.

Frontal Temporal Parietal Occipital

conscious intellect – solving complex, multitask problems

primary motor area – consciously move skeletal muscles

Broca’s area – ability to speak

working memory

auditory

memory

olfactory

somatic sensory area – receives general sensory information from skin and skeletal muscle

visual area

Lateralization of Cortical Functioning – We use both hemispheres for almost every activity and the hemispheres are almost identical. Hemispheres communicate almost instantaneously via fiber tracts and functional integration.

Left hemisphere - Controls language, math, and logic

Right hemisphere - Visual-spatial skills, intuition, emotion, and artistic and musical skills

Limbic system – involves cerebral and diencephalon structures that control emotions and memory o Amygdala – recognizes, assesses danger & elicits

fear response; plays a role in memory processing

o Hippocampus – plays a role in memory processing

Cerebral medulla – inner surface consist of WHITE MATTER (myelinated fiber tracts); responsible for communication between cerebral areas and between the cerebral cortex and lower CNS centers.

Basal nuclei – islands of gray matter within white matter Influence muscle movements -important in starting, stopping and monitoring the intensity of

movements executed by the cortex; regulate intensity of slow movements (ex. swinging arms during walking)

Diencephalon Thalamus – gateway to the cerebral cortex sorts, edits and

relays ascending input. Afferent impulses from all senses and body converge on thalamus before passing upward to the cortex.

Epithalamus – contains the pineal gland which regulates day and night cycles.

Hypothalamus – an important ANS center because it regulates body temperature, water balance and metabolism. It is considered part of the limbic system as it serves as the center for drives & emotions. It regulates the pituitary gland and produces two hormones.

Cerebellum The cerebellum provides precise timing and appropriate patterns of skeletal muscle contraction for smooth, coordinated movements and agility.

Parkinson's disease - degeneration of dopamine-releasing neurons basal nuclei deprived of dopamine become overactive tremors at rest.

Huntington's disease - fatal hereditary disorder caused by accumulation of protein huntingtin leads to degeneration of basal nuclei and cerebral cortex. Symptoms include jerky movements, mental deterioration and treatments include drugs that block dopamine effects.

Alzheimer's disease (AD): a progressive degenerative disease of brain that results in dementia; memory loss, short attention span, disorientation, eventual language loss, irritable, confused

Corpus Collosum – large fiber tract (commissures) that connect gray areas of two hemispheres, enabling them to function as a coordinated whole.

o Damage to ventral root results in inability to stimulate muscles (paralysis)

o Damage to dorsal root results in inability to send stimuli to CNS

Brainstem The brain stem regions are the midbrain, pons and medulla oblongata. Brain stem centers control automatic behaviors necessary for survival and contain fiber tracts connecting higher and lower neural centers. Midbrain – contains tracts that convey ascending &

descending impulses and reflex centers for vision & hearing Pons – contains tracts involved in the control of breathing Medulla Oblongata – merges with the spinal cord; tracts

contain centers to regulate vital visceral activities and centers to control heart rate, blood pressure, breathing, vomiting, etc.

SPINAL CORD – The spinal cord is a continuation of the

brain stem with a two-way conduction pathway to & from the brain and serves as a reflex center.

Protection of CNS Bone - The skull and the vertebral column enclose the brain and spinal cord.

Meninges – connective tissue membranes covering CNS. dura mater – attached to bone and covering the brain & spinal cord arachnoid mater – middle layer has space filled with cerebrospinal fluid (CSF) pia mater – clings to brain and spinal cord

Cerebrospinal Fluid (CSF) – forms a watery cushion that gives buoyancy to the CNS structures; protects the CNS from injury & nourishes the brain

Brainste

m

Developmental Aspects of CNS Gender-specific areas appear in both brain and spinal cord, depending on presence or absence of fetal

testosterone

Age brings some cognitive declines, but not significant in healthy individuals until 80s

Shrinkage of brain accelerates in old age

Hypothalamus one of last areas of CNS to develop -- premature infants poor body temperature regulation

PERIPHERAL NERVOUS SYSTEM (PNS) Nerve – consist of a bundle of myelinated and nonmyelinated peripheral axons enclosed by connective tissue. o Each fiber is surrounded by endoneurium, a loose

connective tissue. o Groups of fibers are bound into bundles called fascicles by

a connective tissue wrapping called perineurium. o All fascicles are enclosed by the epineurium to form the

nerve. Reflexes - Inborn (intrinsic) reflex are rapid, involuntary, predictable motor response to stimulus (ex. maintain posture, control visceral activities). Intrinsic reflexes can be modified by learning and conscious effort. Components of a reflex arc: receptor, sensory neuron, integration center, motor neuron, effector.

Developmental Aspects of Nervous System

System is formed in 1st month of embryonic development. The hypothalamus is the last to mature. Few neurons are formed after birth, but growth and maturation continues all through childhood, mostly as a result of myelination. The brain reaches it max weight as an adult, as we age, neurons are damaged and die. However, neural pathways are always available and being developed.

Nervous tissue has the highest metabolic rate in the body so lack of oxygen for a few minutes leads to death of neurons. Cerebral Palsy may be caused by a temporary lack of oxygen to the brain resulting in poor control of voluntary muscles.

NERVE

Homeostatic Imbalances of the Brain Meningitis – inflammation of the meninges caused by virus or bacteria. Brain inflammation is called encephalitis. Concussion – occurs when brain injury is slight; temporary alteration in function. Contusion – brain injury causing tissue destruction; permanent damage.

After head injuries, death may occur due to intracranial hemorrhage (bleeding of ruptured blood vessels) or cerebral edema (swelling of brain).

Cerebrovascular Accident (CVA) or Stroke – occurs when blood circulation to brain is blocked either by blood clot or ruptured blood vessel. Transient Ischemic Attack (TIA) – is caused from temporary restriction of blood flow; warning for stroke Hydrocephalus – CSF drainage is obstructed and fluid accumulates exerting pressure on the brain. Anencephaly – failure of cerebrum to develop resulting in a child who cannot hear, see or process sensory inputs and development of Spina bifida where the vertebrae form incompletely