ANATOMY & PHYSIOLOGY

FUNCTIONS:

1. Sensory input2. Integration3. Homeostasis4. Mental activity5. Control of muscles and gland

DIVISIONS OF THE NERVOUS SYSTEM:

CENTRAL NERVOUS SYSTEM

Brain & spinal cord

PERIPHERAL NERVOUS SYSTEM

Outside the CNS; consist of nerves & ganglia With 2 divisions:

1. SENSORY/AFFERENTConducts action potentials from sensory receptors to the CNS (sensory neurons)

2. MOTOR/EFFERENTConducts action potentials from the CNS to effector organs such as muscles and glands (motor neurons)

AUTONOMIC NERVOUS SYSTEM – which transmits action potentials from CNS to cardiac muscles, smooth muscles and glands.

1. Sympathetic2. Parasympathetic

CELLS OF THE NERVOUS SYSTEM

Neurons & neuralgia

NEURONS Nerve cells Receive stimuli and transmit action potentials to the neurons or to effector organs. Consist of cell body and 2 types of processes: dendrites & axon Contains a single nucleus – source of information for protein synthesis Extensive rough endoplasmic reticulum, golgi apparatus and mitochondria surround the nucleus NISSL BODIES – areas of rough ER concentration, when stained with a specific dye, appear as

microscopic granules. DENDRITES

Short, often highly branching cytoplasmic extensions that are tapered from their bases at neuron cell body to their tips.

Function to receive information from other neurons or from sensory inputs and transmit the information toward the neuron cell body.

AXON Long process extending from the neuron cell body. Axon Hillock – area where the axon leaves the neuron cell body. May remain branched or unbranched to form COLLATERAL AXONS. SCHWANN CELLS – surrounds axon, which form a highly specialized insulating layer of cells called

myelin sheath.

TYPES OF NEURONS

1. MULTIPOLAR NEURONSHave many dendrites and a single axon

2. BIPOLAR NEURONHave two processes : one dendrite, one axon.Located in some sensory organs: retina of the eye, nasal cavity

3. UNIPOLAR NEURONSHave a single process extending from the cell bodyOne process extends to the periphery, and the other process extends to the CNS.

NEUROGLIA

Nonneuronal cells of CNS & PNS. Far more numerous than neurons: Most neuralgia retain the ability to divide.

TYPES:1. ASTROCYTES – serve as the major supporting tissue in the CNS and participate with the blood vessel

endothelium to form a permeability barrier called the blood-brain barrier, between the blood and the neurons.

2. EPENDYMAL –cells line in the fluid cavities within the CNS. Produce CSF and others, with cilia on the surface, help move the CSF through the CNS.

3. MICROGLIA – help remove bacteria and cell debris from the CNS.4. OLIGODENDROCYTES – cells with many dendiritic processes in the CNS and Schwann cells in the PNS

surround axons. Schwann cells are also called neurolemmocytes, neurolemma cells

MYELIN SHEATHS

UNMYELINATED AXONS - rest in indentations of the oligodendrocytes in the CNS and the Schwann cells in the PNS

MYELINATED AXONS – have specialized sheaths, called myelin sheaths NODES OF RANVIER – gaps in the myelin sheath

ELECTTRIC SIGNALS AND NEURAL PATHWAYS

THE RESTING MEMBRANE POTENTIAL

All cells exhibit electrical properties Outside of most cell membranes is positively charged compared with the inside of the cell membrane, which

is negatively charged. This charge difference across the membrane of an unstimulated cell is called the resting membrane potential,

the call is said to be polarized. The resting membrane potential results from differences in the concentration of ions across the cell

membrane and the permeability characteristics of the cell membrane. At equilibrium, there is a net positive charge outside the cell and a net negative charge inside the cell.

ACTION POTENTIALS

Muscle and nerve cells are excitable. When a stimulus is applied to a muscle cell or nerve cell, some Na channels open for a very brief time, and Na

diffuse quickly into the cell. The movements of Na into a cell is called a local current.

The positively charged Na entering into a cell cause the inside of the cell membrane to become more positive, a change called depolarization, this results in local potential.

SALTATORY CONDUCTION – action potentials jump from one node of ranvier to the next along the length of the axon. This greatly increases the conduction velocity.

THE SYNAPSE

A junction where the axon of one neuron interacts with another neuron or an effector organ.

NEUROTRANSMITTERS

SUBSTANCE LOCATION EFFECT CLINICAL EXAMPLEAcetylcholine

Norepinephrine

Serotonin

Dopamine

Gamma-aminobutyric acid (GABA)

Glycine

Many nuclei scattered throughout the brain & spinal cord. Nerve tracts from the nuclei extend to many areas of the brain and spinal cord. Also found in the neuromuscular junction of skeletal muscle and many ANS synapse

A small number of small sized nuclei in the brainstem. Nerve tracts extend from the nuclei to many areas of the brain and spinal cord. Also in some ANS synapses.

A small number of small sized nuclei in the brainstem. Nerve tracts extend from the nuclei to many areas of the brain and spinal cord.

Confined to a small number of nuclei and nerve tracts. Distribution is more restricted than that of NE or serotonin. Also found in some ANS synapses.

Mostly control activities In their own area and are not usually involved in with transmission from one part of the CNS to another. Most neurons of the CNS have GABA receptors.

Spinal cord and brain. Like GABA, glycine predominantly produces

Excitatory or inhibitory

Excitatory or inhibitory

Generally inhibitory

Generally excitatory

Generally inhibitory

Generally inhibitory

Alzheimer’s disease (a type of senile dementia) is associated with a decrease in acetylcholine secreting neurons. Myasthenia gravis (weakness of skeletal muscle) results from a reduction in acetylcholine receptors.

Cocaine and amphethamines increase the release and block the reuptake of NE, resulting in overstimulation of postsynaptic neurons.

Involved with mood, anxiety, and sleep induction. Levels of serotonin are elevated in schizophrenia (delusions, hallucinations and withdrawal)

Parkinson’s disease (depression of voluntary motor control) results from destruction of dopamine-secreting neurons. Drugs used to increase dopamine production induce vomiting and schizophrenia

Drugs that increase GABA function have been used to treat epilepsy (excessive discharge of neurons).

Glycine receptors are inhibited by the poison strychinine. Strychnine

Endorphins

local effects.

Widely distributed in the CNS & PNS

Generally inhibitory

increases the excitability of certain neurons by blocking their inhibition. Strychnine poisoning results in the powerful muscle contractions and convulsions. Tetanus of respiratory muscles can cause death.

The opiates morphine and heroin bind to endorphin receptors on presynaptic neurons and reduce pain by blocking the release of neurotransmitter.

REFLEXES

Involuntary reaction in response to a stimulus applied to periphery and transmitted to the CNS. REFLEX ARC – neuronal pathway which a reflex occurs.

COMPONENTS:1. Sensory receptors 2. Sensory neuron3. Interneuron4. Motor neuron5. Effector organ

NEURONAL PATHWAYS

CONVERGING PATHWAYS – have two or more neurons that synapse with (converge on) the same neuron. This allows information transmitted in more than one neuronal pathway to converge into a single pathway.

DIVERGING PATHWAYS – the axon from one neuron divides (diverges) and synapses with more than one other neurons. This allows information transmitted in one neuronal pathway to diverge into two or more pathways.

SPINAL CORD

Extends from the foramen magnum at the base of the skull to the 2nd lumbar vertebra. Cauda equina – inferior end of spinal cord.

PLEXUS OF THE SPINAL NERVES

PLEXUSES ORIGIN MAJOR NERVES MUSCLES INNERVATED

SKIN INNERVATED

Cervical

BRACHIAL

C1-C4

C5-T1Phrenic

Axillary

Radial

Several neck musclesDiaphragm

Two shoulder musclesPosterios arm and forearm muscles (extensors)

Neck & posterior head

Part of shoulder

Posterior arm, forearm and hand

Lumbosacral L1-S4

Musculocutaneous

Ulnar

Median

Obturator

Femoral

Ischiadic (sciatic) tibial

Common fibular

Anterior arm muscles (flexors)Two anterior forearm muscles (flexors), most intrinsic hand muscleMost anterior forearm muscles (flexors), some intrinsic hand muscles

Medial thigh muscles (adductors)Anterior muscles (extensions)Posterior thigh muscles (flexors), anterior and posterior leg muscles, most foot musclesLateral thigh and leg, some foot muscles

Radial surface of forearmUlnar side of hand

Radial side of hand

Medial thigh

Anterior thigh

Posterior leg & sole of feet

Anterior and lateral leg, and dorsal (top) part of foot

BRAIN

BRAINSTEM

Connects the spinal cord to the remainder of the brain. Consists of medulla oblongata, pons and midbrain

MEDULLA OBLONGATA

Most inferior portion of brainstem & is continuous with the spinal cord. Extends from the level of foramen magnum to the pons. Functions such as regulation of heart rate and blood vessel diameter, breathing, swallowing, vomting,

coughing, sneezing, balance & coordination.

PONS

Superior to medulla oblongata Relay information between cerebellum and cerebrum Functions such as breathing, swallowing and balance are controlled in the lower pons, as well as in the

medulla oblongata. Other nuclei in pons functions such as chewing and salivation.

MIDBRAIN

Just superior to the pons Smallest region of brainstem Dorsal part of the midbrain consists of four mounds called the colliculi. 2 inferior colliculi are major relay centers for the auditory nerve pathways in the CNS. 2 other involved in visual reflexes. With substantia nigra – regulation of body movements

RETICULAR FORMATION

Scattered throughout the brainstem of group of nuclei Plays important regulatory functions in the brain Regulates cyclical motor functions: respiration, chewing, walking RETICULAR ACTIVATING SYSTEM –arousing and maintaining consciousness and in regulating the sleep-wake

cycle. Damage to cells of the reticular formation can result in coma.

CEREBELLUM

Little brain Cerebellar peduncles – provide routes of communication between the cerebellum and other parts of the CNS. Coordination of muscular contraction – maintenance of balance

DIENCEPHALON

Between brainstem and cerebrum Main components: thalamus, epithalamus, hypothalamus1. THALAMUS

Largest part of diencephalon consists