BackBIO 163: Nervous System and Special Senses Study Guide
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Chapter 7: The Nervous System
Overview and Functions of the Nervous System
The nervous system is responsible for coordinating the body's responses to internal and external stimuli. It achieves this through three overlapping functions:
Sensory Input: Gathering information from sensory receptors about changes inside and outside the body.
Integration: Processing and interpreting sensory input to determine an appropriate response.
Motor Output: Activating effector organs (muscles and glands) to cause a response.
Organization of the Nervous System
Central Nervous System (CNS): Consists of the brain and spinal cord; responsible for integration and command.
Peripheral Nervous System (PNS): Consists of cranial and spinal nerves; connects the CNS to the rest of the body.
The PNS is further divided into:
Sensory (Afferent) Division: Transmits impulses from sensory receptors to the CNS.
Motor (Efferent) Division: Transmits impulses from the CNS to effector organs.
The Motor Division is subdivided into:
Somatic Nervous System: Voluntary control of skeletal muscles.
Autonomic Nervous System: Involuntary control of smooth muscle, cardiac muscle, and glands.
Neuroglia (Glial Cells)
Neuroglia are supporting cells in the nervous system. They do not conduct nerve impulses but provide structural and functional support.
CNS Neuroglia:
Astrocytes: Maintain the blood-brain barrier, regulate nutrient and ion concentrations.
Microglial Cells: Act as phagocytes, removing debris and pathogens.
Ependymal Cells: Line ventricles, produce and circulate cerebrospinal fluid (CSF).
Oligodendrocytes: Form myelin sheaths around CNS axons.
PNS Neuroglia:
Satellite Cells: Surround neuron cell bodies in ganglia, regulate environment.
Schwann Cells: Form myelin sheaths around PNS axons.
Myelin Sheath and Nodes of Ranvier
Myelin Sheath: Insulating layer around axons; increases speed of nerve impulse conduction.
Formed by: Schwann cells in PNS, oligodendrocytes in CNS.
Nodes of Ranvier: Gaps in the myelin sheath; facilitate rapid conduction via saltatory conduction.
Myelinated vs. Unmyelinated: Impulses travel faster in myelinated fibers.
Neurons (Nerve Cells)
Function: Transmit electrical impulses throughout the body.
Structures:
Dendrites: Receive signals from other neurons.
Axon: Conducts impulses away from the cell body.
Axon Hillock: Initial segment where action potentials are generated.
Axon Terminal: Releases neurotransmitters into the synaptic cleft.
Neurotransmitters: Chemical messengers between neurons.
Synaptic Cleft: Gap between neurons where neurotransmitters act.
Multiple Sclerosis
Cause: Autoimmune destruction of myelin sheaths in the CNS.
Effect: Slowed or blocked nerve impulses, leading to muscle weakness and coordination problems.
Key Terms
Ganglia: Clusters of neuron cell bodies in the PNS.
Nuclei: Clusters of neuron cell bodies in the CNS.
Tracts: Bundles of axons in the CNS.
Nerves: Bundles of axons in the PNS.
White Matter: Myelinated axons.
Gray Matter: Unmyelinated cell bodies and dendrites.
Classification of Neurons
Functional: Sensory (afferent), motor (efferent), interneurons (association).
Structural: Multipolar, bipolar, unipolar.
Properties of Nerve Cells
Irritability: Ability to respond to a stimulus and convert it into a nerve impulse.
Conductivity: Ability to transmit the impulse to other neurons, muscles, or glands.
Action Potential (Nerve Impulse)
Resting Membrane Potential (Polarized): The inside of the neuron is negatively charged relative to the outside.
Depolarization: Sodium (Na+) channels open, Na+ enters the cell, making the inside more positive.
Action Potential: If threshold is reached, a rapid change in membrane potential occurs.
Repolarization: Potassium (K+) channels open, K+ leaves the cell, restoring negative charge inside.
All-or-None Response: A neuron either fires completely or not at all.
Equation for Resting Membrane Potential:
Additional info: This is the Nernst equation for potassium, a major determinant of resting potential.
Reflexes and Reflex Arcs
Reflex: Rapid, predictable, involuntary response to a stimulus.
Somatic Reflexes: Involve skeletal muscles.
Autonomic Reflexes: Involve smooth muscle, cardiac muscle, or glands.
Five Elements of Reflex Arc (in order):
Receptor
Sensory Neuron
Integration Center
Motor Neuron
Effector
Brain Structures
Cerebral Hemispheres: Largest part; divided into lobes (frontal, parietal, temporal, occipital).
Diencephalon: Contains thalamus (relay station), hypothalamus (homeostasis), epithalamus.
Brain Stem: Includes midbrain (corpora quadrigemina), pons (respiratory control), medulla oblongata (vital centers).
Cerebellum: Coordinates voluntary movements and balance.
Cerebral Cortex
Lobes: Frontal, parietal, temporal, occipital.
Sulci: Shallow grooves.
Fissures: Deep grooves.
Functional Areas:
Motor Areas: Control voluntary movement (frontal lobe).
Sensory Areas: Receive sensory input (parietal, occipital, temporal lobes).
Association Areas: Integrate information (multiple lobes).
Brain Stem and Diencephalon Structures
Thalamus: Sensory relay station.
Hypothalamus: Regulates homeostasis (temperature, hunger, thirst, endocrine activity).
Epithalamus: Contains pineal gland (melatonin secretion).
Midbrain: Contains cerebral peduncles (fiber tracts), corpora quadrigemina (visual/auditory reflexes).
Pons: Controls breathing rate.
Medulla Oblongata: Controls cardiovascular, respiratory, and other vital centers.
Reticular Activating System: Maintains consciousness and alertness.
Meninges and Cerebrospinal Fluid (CSF)
Meningeal Layers (outer to inner):
Dura mater
Arachnoid mater
Pia mater
Function: Protect the CNS.
CSF: Formed by choroid plexuses; circulates in ventricles and subarachnoid space; cushions the brain and spinal cord.
Blood-Brain Barrier
Function: Protects the brain from harmful substances in the blood while allowing essential nutrients to pass.
Brain and Spinal Cord Injuries
Traumatic Brain Injuries: Concussion, contusion, hemorrhage.
CVA (Stroke): Blockage or rupture of blood vessels; symptoms depend on area affected.
TIA (Transient Ischemic Attack): Temporary reduction in blood flow; warning sign for stroke.
Spinal Cord Anatomy
Gray Matter: Dorsal horns (sensory), ventral horns (motor), dorsal root ganglion (sensory cell bodies).
White Matter: Surrounds gray matter; contains ascending and descending tracts.
Connective Tissue Wrappings: Endoneurium, perineurium, epineurium.
Cranial and Spinal Nerves
Cranial Nerves: 12 pairs; serve head and neck functions.
Spinal Nerves: 31 pairs; each formed by dorsal and ventral roots.
Dorsal Rami: Serve skin and posterior trunk.
Ventral Rami: Form nerve plexuses (except thoracic nerves); serve limbs and anterior trunk.
Plexuses and Major Nerves:
Cervical: Phrenic nerve (diaphragm)
Brachial: Axillary, ulnar, radial nerves (upper limb)
Lumbar: Femoral nerve (anterior thigh)
Sacral: Sciatic nerve (lower limb)
Somatic vs. Autonomic Nervous System
Somatic: Voluntary, one neuron from CNS to effector, targets skeletal muscle.
Autonomic: Involuntary, two-neuron chain, targets smooth/cardiac muscle and glands.
Sympathetic vs. Parasympathetic Divisions
Sympathetic: "Fight or flight"; increases heart rate, dilates pupils, inhibits digestion.
Parasympathetic: "Rest and digest"; decreases heart rate, stimulates digestion, constricts pupils.
Developmental Disorders
Cerebral Palsy: Brain damage during development; causes motor impairment.
Anencephaly: Failure of brain development; incompatible with life.
Spina Bifida: Incomplete closure of spinal column; can cause paralysis.
Chapter 8: Special Senses
External Eye Anatomy
Accessory Structures: Extrinsic eye muscles (move the eye), eyelids (protect), conjunctiva (mucous membrane), lacrimal apparatus (produces tears).
Tarsal and Ciliary Glands: Secrete oils to lubricate the eye.
Lacrimal Apparatus: Produces and drains tears; tears clean and moisten the eye.
Internal Eye Anatomy
Three Layers:
Fibrous Layer: Sclera (white of eye), cornea (transparent, refracts light).
Vascular Layer: Choroid (blood supply), ciliary body (lens shape), iris (controls pupil size).
Sensory Layer (Retina): Pigmented layer (absorbs light), neural layer (photoreceptors: rods and cones).
Photoreceptors: Rods (dim light, black and white), cones (color, sharp vision).
Signal Pathway: Photoreceptors → bipolar cells → ganglion cells → optic nerve → visual cortex.
Optic Disc and Fovea Centralis
Optic Disc: "Blind spot" where optic nerve exits; no photoreceptors.
Fovea Centralis: Area of sharpest vision; high density of cones.
Lens and Eye Segments
Lens: Focuses light on the retina.
Anterior Segment: Contains aqueous humor (nourishes cornea/lens, maintains pressure).
Posterior Segment: Contains vitreous humor (maintains eye shape).
Accommodation and Real Image
Accommodation: Adjustment of lens shape to focus on near or distant objects.
Real Image: Inverted image formed on the retina.
Pupillary Reflexes
Photopupillary Reflex: Pupil constricts in bright light.
Accommodation Pupillary Reflex: Pupil constricts when focusing on close objects.
Visual Pathway
Light passes: Cornea → aqueous humor → lens → vitreous humor → retina → photoreceptors → bipolar cells → ganglion cells → optic nerve → visual cortex.
Homeostatic Imbalances of the Eye
Night Blindness: Poor rod function.
Color Blindness: Lack of one or more cone types.
Myopia: Nearsightedness; image focuses in front of retina.
Hyperopia: Farsightedness; image focuses behind retina.
Presbyopia: Loss of accommodation with age.
Cataracts: Clouding of the lens.
Glaucoma: Increased intraocular pressure damages optic nerve.
Ear Anatomy and Function
Outer Ear: Auricle (pinna), external auditory canal; separated from middle ear by tympanic membrane (eardrum).
Middle Ear: Ossicles (malleus, incus, stapes); transmit vibrations to inner ear.
Inner Ear: Vestibule (static equilibrium), semicircular canals (dynamic equilibrium), cochlea (hearing).
Equilibrium and Hearing
Maculae: Receptors in vestibule; detect head position; otoliths (calcium stones) aid static equilibrium.
Crista Ampullaris: Receptors in semicircular canals; detect rotational movement (dynamic equilibrium); endolymph fluid moves during rotation.
Cochlea: Contains spiral organ (organ of Corti) for hearing.
Types of Deafness
Conduction Deafness: Sound transmission blocked (e.g., earwax, ossicle damage).
Sensorineural Deafness: Damage to hair cells or nerves.
Meniere’s Disease: Inner ear disorder causing vertigo and hearing loss.
Olfaction and Gustation (Smell and Taste)
Olfactory Receptors: Detect chemicals in the air (smell).
Taste Buds: Located on papillae of tongue; contain gustatory cells (taste receptors).
Papillae Types: Filiform, vallate, fungiform, foliate.
Five Basic Tastes: Sweet, sour, salty, bitter, umami.
Special Sense Not Fully Functional at Birth: Vision.
Neuroglia Type | Location | Function |
|---|---|---|
Astrocytes | CNS | Support, blood-brain barrier |
Microglial Cells | CNS | Phagocytosis |
Ependymal Cells | CNS | Produce/circulate CSF |
Oligodendrocytes | CNS | Form myelin sheath |
Satellite Cells | PNS | Support neuron cell bodies |
Schwann Cells | PNS | Form myelin sheath |
Additional info: Table summarizes neuroglia types, locations, and functions for quick review.
