INTRODUCTION TO THE NERVOUS SYSTEM, PNS, CNS

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The Nervous System

The body's control center and communication network; works with the endocrine system to maintain homeostasis.

Peripheral Nervous System (PNS)

Nerves and Ganglia outside the CNS.

Sensory (Afferent)

Carries input to the CNS. Travel from sensory receptors via sensory neurons.

Motor (Efferent)

Carries output from the CNS. Travel via motor neurons toward effector organs.

Somatic System

Voluntary control (skeletal muscles).

Autonomic System

Involuntary control (cardiac/smooth muscles, glands); divided into Sympathetic and Parasympathetic.

Enteric System

Sensory and motor control of the digestive tract.

Neurons (Nerve Cells)

Structural units that receive stimuli and transmit electrical impulses.

Cell Body (Soma)

Part of neuron that contains the nucleus.

Dendrites

Part of neuron that receives input/stimuli.

Axon

Part of neuron that transmits output/impulses away from the cell body. Covered by an insulating Myelin Sheath with gaps called Nodes of Ranvier to speed up transmission.

Multipolar Neuron

most common, many dendrites/one axon. all motor neurons

Bipolar Neuron

one dendrite/one axon; sensory organs. sensory neurons

Pseudounipolar Neuron

single process extending from the cell body that divides into two extensions; Sensory neurons in PNS

Interneurons/Association

between neurons. Function in the integration of impulses.

Neuroglia

Supporting Cells

CNS Glia

Astrocytes, Ependymal Cells, Microglia, Oligodendrocytes

PNS Glia

Schwann Cells, Satellite Cells.

Gray Matter

Cell bodies, dendrites, unmyelinated axons. Found on the brain's surface (cortex) and deep in the spinal cord.

White Matter

Bundles of myelinated axons. Found in CNS nerve tracts and PNS nerves.

Irritability

refers to the ability to respond to a stimulus & to convert it into a NERVE IMPULSE

Conductivity

refers to the ability to transmit this impulse to other neurons, muscles, or glands

Resting Membrane Potential

-60 mV. The inside of the cell is more negative (higher K+) than the outside (higher Na+).

NERVE IMPULSE

Also known as “action potential” A wave of electrical fluctuation that travels along the cell

membrane

Depolarization

Stimulus opens voltage-gated Na+ channels; Na+ rushes in, reversing the membrane potential from negative to positive.

Repolarization

Voltage-gated K+ channels open; K+ rushes out, restoring the negative charge inside.

Restoration

Sodium-potassium pumps restore the exact resting ion concentrations.

Synapses

The region where neurons communicate with other neurons or target effector organs

Axodendritic

axon to dendrite

Axosomatic

axon to cell body

Axoaxonic

axon to axon

Electrical synapses

Conduct through gap junctions (common in cardiac/smooth muscle).

Chemical synapses

Use neurotransmitters (e.g., acetylcholine, dopamine) released via exocytosis into the synaptic cleft to bind to postsynaptic receptors.

Reflexes

are rapid, predictable & involuntary responses to stimuli

Somatic Reflex

Reflex that stimulates skeletal muscles

Autonomic Reflex

Reflexes that regulates the activity of smooth muscles, the heart and glands

Diverging

One neuron branching to affect many.

Converging

Many neurons converging on a single output cell.

Reverberating

Circular feedback loops.

Parallel After-Discharge

Parallel arrays converging on a single output, causing a burst of impulses (complex mental processing).

NERVES

Bundles of neuron fibers / axons found OUTSIDE the CNS

Endoneurium

Covers each individual axon.

Perineurium

Surrounds groups of axons arranged in bundles called fascicles.

Epineurium

Surrounds the entire nerve formed by bundled fascicles.

Cranial Nerves

12 pairs originating or terminating in the brain. Primarily innervate the head and neck, except for CN X (Vagus), which extends into the thorax and abdomen.

12 Cranial Nerves (Oh, Oh, Oh, To Touch And feel Very Good, Velvet. Such Heaven

Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Abducens, Facial, Vestibulocochlear (Acoustic), Glossopharyngeal, Vagus, Accessory, Hypoglossal

Type of function for cranial nerves (Some Say Marry Money But My Brother Says Big Brains Matter Most)

Sensory, Sensory, Motor, Motor, Both, Motor, Both, Sensory, Both, Both, Motor, Motor

Olfactory

Sensory (S), Sense of smell

Optic

Sensory (S), Vision

Oculomotor

Motor, Extraocular eye movement (4 of 6 extrinsic muscles), upper eyelid elevation, pupillary constriction, lens thickening

Trochlear

Motor (M), Upward & downward eye movement (motor to 1 extrinsic eye muscle)

Trigeminal

Both (S, M / B), Sensory to face, teeth, and mouth; motor to muscles of mastication (chewing)

Abducens

Motor (M), Lateral eye movement (motor to 1 extrinsic eye muscle)

Facial

Both, Taste (anterior tongue); muscles of facial expression; production of saliva and tears

Vestibulocochlear

Sensory (S), Hearing and balance

Glossopharyngeal

Both, Taste and touch to back of tongue; swallowing; pharyngeal muscles; salivation

Vagus

Both, Sensory to pharynx, larynx, viscera; motor to palate, pharynx, larynx; regulates digestive, respiratory, and cardiovascular activities

Accessory

Motor (M), Head and shoulder movement (motor to two neck and upper back muscles)

Hypoglossal

Motor (M), Tongue movement and swallowing

Spinal Nerves

31 pairs total, formed by the dorsal (posterior/sensory) and ventral (anterior/motor) roots of the spinal cord.

Posterior Horn

Contains interneurons and sensory axons.

Anterior Horn

Contains somatic motor neurons.

Lateral Horn

Contains autonomic motor neurons.

Dermatomes

Defined as a specific area of skin supplied with sensory innervation by a pair of spinal nerves.

Nerve Plexuses

Complex networks of nerves serving the motor and sensory needs of the limbs/extremities.

Cervical Plexus

(C1–C4), Innervates muscles attached to the hyoid bone and neck.

Brachial Plexus

(C5–T1), Supplies nerves to the shoulder and upper limbs.

Axillary

Shoulder muscles/skin.

Radial

Posterior arm/forearm extensors.

Musculocutaneous

Anterior arm flexors.

Median & Ulnar

Anterior forearm flexors and intrinsic hand muscles.

Lumbosacral Plexus

(L1–S4), Provides innervation to the lower limbs.

Obturator

Medial thigh (adductors).

Femoral

Anterior thigh (extensors).

Tibial & Common Fibular

Posterior/lateral leg and foot muscles.

Phrenic nerve

innervates the diaphragm

The Autonomic Nervous System (ANS)

Innervates smooth muscle, cardiac muscle, and glands under involuntary control.

Preganglionic Neuron

Extends from CNS to an autonomic ganglion.

Postganglionic Neuron

Extends from the ganglion to the effector organ.

Somatic Nervous System

Single myelinated motor neuron directly reaching skeletal muscle without a ganglion.

Autonomic Nervous System

Two-neuron series (myelinated preganglionic leading to an unmyelinated postganglionic neuron via a ganglion).

Sympathetic Division (SNS)

"Fight-or-flight" / Prepares body for physical activity & alertness

Parasympathetic Division (PSNS)

"Rest-and-digest" / Body at rest, conserves energy, handles digestion

Autonomic Effects on Heart

SNS increases rate/force; PSNS decreases rate.

Autonomic Effects on Lungs

SNS dilates bronchioles; PSNS constricts bronchioles.

Autonomic Effects on Pupils

SNS dilates; PSNS constricts.

Autonomic Effects on Digestive Tract

SNS decreases motility/inhibits secretion; PSNS increases motility/relaxes sphincters.

The Enteric Nervous System (ENS)

Consists of local networks of plexuses located entirely within the walls of the digestive tract.

Sensory Neurons

Connect the digestive tract to the CNS.

Autonomic Neurons

Sympathetic and parasympathetic fibers linking the CNS to the gut.

Enteric Neurons

Local circuit neurons within the enteric plexus (myenteric and submucosal plexuses) that monitor and control the digestive tract independently of the CNS via local reflexes.

CENTRAL NERVOUS SYSTEM

a major structural division of the nervous system. consists of the BRAIN and SPINAL CORD

BRAIN

a complex organ of the CNS composed primarily of nervous tissue contained within the cranium. controls vital body functions: temperature, heart rate, respiration, BP, thinking, emotions, sensory and motor activities

Brainstem

a major region of the brain connected superiorly to the spinal cord consist of the medulla oblongata, pons and midbrain. Regulates cardiovascular/respiratory functions; intermediate pathway for sensorimotor info between spinal cord and higher brain centers

Basilar Artery

Formed by the union of the two vertebral arteries.

Circle of Willis

(Cerebral Arterial Circle): Formed by the junction of the internal carotid and basilar arteries to supply various brain regions.

Internal carotid arteries.

supply the majority of blood to the brain

Medulla Oblongata

Most inferior region of brainstem; extends from foramen magnum to pons; continuous with spinal cord.

Ascending tract

transmit sensory info from SC to brain

Descending tract

motor info from brain to SC