Study Guide: The Nervous System (ANP College Level)

Nervous System Overview

Functions of the Nervous System

The nervous system is the master controlling and communicating system of the body. It enables rapid communication between cells via electrical and chemical signals, allowing the body to respond to internal and external changes.

• Sensory Input: Gathering information about internal and external environments.

• Integration: Processing and interpretation of sensory input.

• Motor Output: Activation of effector organs (muscles and glands) to produce a response.

• Example: Seeing a glass of water (sensory input), deciding to pick it up (integration), and moving your arm (motor output).

Organization of the Nervous System

The nervous system is divided into two main parts: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

• Central Nervous System (CNS): Consists of the brain and spinal cord. It interprets sensory input and dictates motor output.

• Peripheral Nervous System (PNS): Composed of nerves that extend from the brain and spinal cord. It connects the CNS to the rest of the body.

Functional Divisions of the PNS

The PNS is further divided into sensory (afferent) and motor (efferent) divisions. The motor division includes the somatic and autonomic nervous systems.

• Sensory (Afferent) Division: Conducts impulses from sensory receptors to the CNS.

• Motor (Efferent) Division: Conducts impulses from the CNS to effector organs.

• Somatic Nervous System: Controls voluntary movements of skeletal muscles.

• Autonomic Nervous System (ANS): Regulates involuntary functions (smooth muscle, cardiac muscle, glands). Includes sympathetic (activates body systems) and parasympathetic (conserves energy) divisions.

Neurons and Neuroglia

Structure and Function of Neurons

Neurons are the structural and functional units of the nervous system. They are specialized for transmitting electrical impulses.

• Extreme Longevity: Neurons can live for a lifetime.

• High Metabolic Rate: Require continuous supply of oxygen and glucose.

• Processes: Neurons have one or more processes (dendrites and axons).

Neuron Anatomy

Each neuron consists of a cell body (soma), dendrites, and an axon.

• Cell Body: Biosynthetic center; synthesizes proteins, membranes, and chemicals.

• Dendrites: Receptive regions; convey incoming messages toward the cell body.

• Axon: Conducting region; generates and transmits nerve impulses to axon terminals.

• Axon Terminals: Secrete neurotransmitters to communicate with other neurons or effector cells.

Myelin Sheath

The myelin sheath is a protective covering around axons that increases the speed of nerve impulse transmission.

• Myelinated Fibers: Have segmented sheaths; transmit impulses rapidly.

• Nonmyelinated Fibers: Lack myelin; transmit impulses more slowly.

Classification of Neurons

Neurons are classified structurally based on the number and arrangement of their processes:

• Multipolar: Three or more processes (one axon, multiple dendrites); most common in CNS.

• Bipolar: Two processes (one axon, one dendrite); found in special sensory organs.

• Unipolar: One T-like process; found mainly in PNS.

Neuron Type	Processes	Location
Multipolar	1 axon, multiple dendrites	CNS
Bipolar	1 axon, 1 dendrite	Special senses
Unipolar	Single T-like process	PNS

Central Nervous System: Brain and Spinal Cord

Brain Regions

The brain is divided into several major regions, each with distinct functions:

• Cerebral Hemispheres: Responsible for higher brain functions.

• Diencephalon: Includes thalamus, hypothalamus, and epithalamus.

• Brain Stem: Includes midbrain, pons, and medulla oblongata; controls basic life functions.

• Cerebellum: Coordinates movement and balance.

Cerebral Hemispheres and Lobes

The cerebral hemispheres are divided into lobes named after the overlying skull bones: frontal, parietal, temporal, occipital, and the insular lobe (buried under portions of other lobes).

Cerebral Cortex

The cerebral cortex is the site of conscious mind, including awareness, perception, voluntary movement, and communication.

• Motor Areas: Located in the frontal lobe; control voluntary movement.

• Broca’s Area: Directs muscles of speech production; involved in planning speech.

• Frontal Eye Field: Controls voluntary eye movements.

• Primary Somatosensory Cortex: Receives sensory information from skin, skeletal muscle, joints, and tendons; enables spatial discrimination.

• Somatosensory Association Cortex: Integrates sensory input to determine size, texture, and relationship of objects.

• Primary Visual Cortex: Receives information from retinas; interprets visual stimuli.

• Primary Auditory Cortex: Interprets information from inner ear as pitch, loudness, and location.

• Auditory Association Area: Stores memories of sounds and permits perception of sound stimulus.

• Primary Olfactory Cortex: Involved in conscious awareness of odors.

• Gustatory Cortex: Involved in perception of taste.

• Visceral Sensory Area: Conscious perception of visceral sensations.

• Wernicke’s Area: Involved in understanding written and spoken language.

The Diencephalon

The diencephalon consists of the thalamus, hypothalamus, and epithalamus.

• Thalamus: Sorts, edits, and relays input; mediates sensation, motor activities, cortical arousal, learning, and memory.

• Hypothalamus: Regulates body temperature, hunger, thirst, sleep-wake cycles, and controls pituitary gland secretions.

• Epithalamus: Contains the pineal gland, which secretes melatonin.

Brain Stem

The brain stem is composed of the midbrain, pons, and medulla oblongata. It controls basic life functions and serves as a pathway for information between the brain and spinal cord.

• Midbrain: Controls cranial nerves III and IV; involved in fight or flight response.

• Pons: Connects higher brain centers and spinal cord; relays impulses between motor cortex and cerebellum; helps with breathing.

• Medulla Oblongata: Autonomic reflex center; controls heart rate, blood vessel diameter, respiratory rhythm, and other vital functions.

Cerebellum

The cerebellum coordinates movements of skeletal muscles and maintains balance.

Limbic System

The limbic system is involved in emotional responses, memory, and psychosomatic illnesses.

• Amygdaloid Body: Recognizes angry or fearful facial expressions.

• Cingulate Gyrus: Expresses emotions via gestures and resolves mental conflict.

• Hippocampus: Involved in memory formation.

Corpus Callosum

The corpus callosum is the major connection between the two cerebral hemispheres, allowing communication between them.

Protection of the Brain

The brain is protected by three layers of meninges: dura mater, arachnoid mater, and pia mater. These layers provide physical protection, support, and nourishment.

• Dura Mater: Tough, outermost layer.

• Arachnoid Mater: Middle layer; contains cerebrospinal fluid.

• Pia Mater: Delicate, innermost layer.

Peripheral Nervous System

Peripheral Nervous System Overview

The PNS consists of nerves and ganglia outside the CNS. It connects the CNS to limbs and organs.

Classification by Stimulus Type

• Mechanoreceptors: Respond to mechanical force.

• Thermoreceptors: Respond to temperature changes.

• Photoreceptors: Respond to light.

• Chemoreceptors: Respond to chemicals.

• Nociceptors: Respond to pain.

Cranial Nerves

There are 12 pairs of cranial nerves, each with specific sensory and motor functions.

Cranial Nerve	Sensory Function	Motor Function	Parasympathetic Fibers
I: Olfactory	Yes (smell)	No	No
II: Optic	Yes (vision)	No	No
III: Oculomotor	No	Yes	Yes
IV: Trochlear	No	Yes	No
V: Trigeminal	Yes (general sensory)	Yes	No
VI: Abducens	No	Yes	No
VII: Facial	Yes (taste)	Yes	Yes
VIII: Vestibulocochlear	Yes (hearing and balance)	Some	No
IX: Glossopharyngeal	Yes (taste)	Yes	Yes
X: Vagus	Yes	Yes	Yes
XI: Accessory	No	Yes	No
XII: Hypoglossal	No	Yes	No

Spinal Nerves

There are 31 pairs of spinal nerves that supply all body parts except the head and part of the neck.

• 8 pairs of cervical nerves (C1–C8)

• 12 pairs of thoracic nerves (T1–T12)

• 5 pairs of lumbar nerves (L1–L5)

• 5 pairs of sacral nerves (S1–S5)

• 1 pair of coccygeal nerves (C0)

Summary Table: Structural Classes of Neurons

Neuron Type	Processes	Location	Function
Multipolar	1 axon, multiple dendrites	CNS	Motor and interneurons
Bipolar	1 axon, 1 dendrite	Special senses	Sensory
Unipolar	Single T-like process	PNS	Sensory

Additional info: Academic context was added to clarify the functions, structure, and classification of neurons, as well as the organization and protection of the nervous system.