Central and Peripheral Nervous Systems, Autonomic Nervous System, and Special Senses: Study Guide

Central Nervous System (CNS)

Brainstem: Parts and Functions

The brainstem is a critical structure connecting the brain and spinal cord, responsible for many automatic functions necessary for survival.

• Midbrain: Controls visual and auditory reflexes, and coordinates movement.

• Pons: Relays information between the cerebrum and cerebellum; regulates breathing.

• Medulla oblongata: Controls vital autonomic functions such as heart rate, blood pressure, and respiration.

Example: Damage to the medulla can result in loss of respiratory function.

Cerebellum: Anatomy and Function

The cerebellum is located at the back of the brain and is essential for coordination, balance, and fine motor control.

• Receives sensory input about body position and movement.

• Coordinates voluntary movements and maintains posture.

Example: Cerebellar damage can cause ataxia, a loss of coordination.

Protection of the Brain

• Meninges: Three connective tissue layers that protect the CNS:

  • Dura mater: Tough, outermost layer.

  • Arachnoid mater: Middle, web-like layer.

  • Pia mater: Delicate, innermost layer adhering to the brain surface.

• Cerebrospinal fluid (CSF): Cushions the brain, provides nutrients, and removes waste.

• Blood-brain barrier: Selectively allows substances to pass from blood to brain tissue, protecting against toxins and pathogens.

Brain Injuries and Disorders

• Concussion: Temporary brain dysfunction due to trauma; symptoms include headache, confusion, and dizziness.

• Contusion: Bruising of brain tissue, often with more severe and lasting effects than concussion.

• Cerebrovascular accident (CVA or stroke): Disruption of blood flow to the brain, causing tissue death; symptoms depend on the affected area.

Spinal Cord: Anatomy and Function

• Gross anatomy: Extends from the foramen magnum to the lumbar region; protected by vertebrae, meninges, and CSF.

• Microscopic anatomy: Contains gray matter (cell bodies) and white matter (myelinated axons).

• Roots: Dorsal (sensory) and ventral (motor) roots join to form spinal nerves.

• Ganglia: Clusters of sensory neuron cell bodies outside the CNS.

• Function: Transmits sensory and motor information; mediates reflexes.

Spinal Cord Diseases and Trauma

• Injuries can result in paralysis or loss of sensation below the site of damage.

• Diseases include multiple sclerosis, amyotrophic lateral sclerosis (ALS), and spinal cord tumors.

Key Vocabulary

• Fissure: Deep groove in the brain.

• Gyrus: Raised ridge on the brain surface.

• Sulcus: Shallow groove between gyri.

• Lateralization: Specialization of brain function in one hemisphere.

• Contralateral: Opposite side control (e.g., left brain controls right body).

• Homunculus: Map of body regions on the cortex.

• Motor cortex: Controls voluntary movements.

• Somatosensory cortex: Processes sensory input from the body.

• Meninges, concussion, contusion, cerebrovascular accident: See above.

Peripheral Nervous System (PNS)

Divisions of the PNS

The PNS connects the CNS to the rest of the body and is divided into:

• Somatic nervous system: Controls voluntary movements via skeletal muscles.

• Autonomic nervous system (ANS): Regulates involuntary functions (see below).

Classification of Receptors

• By function:

  • Mechanoreceptors: Detect mechanical forces (touch, pressure).

  • Thermoreceptors: Detect temperature changes.

  • Photoreceptors: Detect light (in the eye).

  • Chemoreceptors: Detect chemicals (taste, smell).

  • Nociceptors: Detect pain.

• By location:

  • Exteroceptors: Respond to stimuli outside the body.

  • Interoceptors: Respond to internal stimuli.

  • Proprioceptors: Detect body position and movement.

Structure and Classification of Nerves

• Nerve: Bundle of axons in the PNS.

• Classification:

  • Sensory (afferent) nerves: Carry information to the CNS.

  • Motor (efferent) nerves: Carry commands from the CNS.

  • Mixed nerves: Contain both sensory and motor fibers.

Connective Tissue Layers of Nerves

• Epineurium: Outermost layer, surrounds the entire nerve.

• Perineurium: Surrounds bundles (fascicles) of axons.

• Endoneurium: Surrounds individual axons.

Key Vocabulary

• Sensation: Awareness of a stimulus.

• Perception: Interpretation of sensory input.

• Pain: Unpleasant sensory experience.

• Pain tolerance: Maximum pain level a person can endure.

• Somatic afferent: Sensory signals from skin, muscles, joints to CNS.

• Somatic efferent: Motor signals from CNS to skeletal muscles.

• Visceral afferent: Sensory signals from organs to CNS.

• Visceral efferent: Motor signals from CNS to organs.

Autonomic Nervous System (ANS)

Definition and Comparison to Somatic Nervous System

The autonomic nervous system (ANS) controls involuntary functions such as heart rate, digestion, and respiratory rate. It differs from the somatic nervous system, which controls voluntary muscle movements.

• Somatic: One neuron from CNS to muscle; always excitatory.

• Autonomic: Two-neuron chain (preganglionic and postganglionic); can be excitatory or inhibitory.

Efferent Pathways

• Preganglionic neuron: Cell body in CNS; axon extends to autonomic ganglion.

• Postganglionic neuron: Cell body in ganglion; axon extends to effector organ.

Neurotransmitters in the ANS

• Acetylcholine (ACh): Released by all preganglionic neurons and parasympathetic postganglionic neurons.

• Norepinephrine (NE): Released by most sympathetic postganglionic neurons.

Sympathetic vs. Parasympathetic Divisions

Feature	Sympathetic	Parasympathetic
Origin	Thoracolumbar (T1-L2)	Craniosacral (brainstem, S2-S4)
Function	"Fight or flight" (increases HR, dilates pupils, inhibits digestion)	"Rest and digest" (decreases HR, constricts pupils, stimulates digestion)
Neurons	Short preganglionic, long postganglionic	Long preganglionic, short postganglionic
Neurotransmitter	NE (postganglionic)	ACh (postganglionic)

• Dual innervation: Most organs receive input from both divisions, allowing precise control.

• Dynamic antagonism: The two divisions often have opposing effects, maintaining homeostasis.

Key Vocabulary

• Involuntary nervous system: Another term for ANS.

• Effectors: Organs, glands, or muscles acted upon by the ANS.

• Dual innervation, dynamic antagonism, craniosacral, thoracolumbar: See above.

Special Senses

Overview of Special Senses

• Vision

• Hearing (audition)

• Equilibrium (balance)

• Taste (gustation)

• Smell (olfaction)

Sound Conduction Pathway

• Sound waves enter the external ear and vibrate the tympanic membrane.

• Vibrations are transmitted through the ossicles (malleus, incus, stapes) to the oval window.

• Movement of the oval window creates waves in the cochlear fluids.

Anatomy of the Cochlea

• Cochlea: Spiral-shaped organ containing the organ of Corti (hearing receptor cells).

• Divided into three chambers: scala vestibuli, scala media, and scala tympani.

Auditory Pathway

• Hair cells in the organ of Corti transduce mechanical vibrations into nerve impulses.

• Impulses travel via the cochlear nerve to the brainstem, then to the auditory cortex.

Equilibrium: Semicircular Canals and Vestibule

• Semicircular canals: Detect rotational (angular) movements.

• Vestibule (saccule and utricle): Detect linear acceleration and head position.

• Vestibular apparatus: Includes semicircular canals and vestibule; maintains balance.

Key Vocabulary

• Sound detection: Process of converting sound waves into electrical signals.

• Equilibrium: Sense of balance.

• Vestibular apparatus, saccule, utricle, ampulla, maculae, crista ampullaris: Structures involved in balance.

• Nystagmus: Involuntary eye movement, often related to vestibular dysfunction.

• Benign paroxysmal positional vertigo (BPPV): Common cause of vertigo due to displaced otoliths in the inner ear.

• Motion sickness: Sensory conflict between visual and vestibular inputs.

Additional info: This guide expands on the provided review topics with academic context and definitions to ensure a comprehensive understanding for exam preparation.