Nervous System, CNS, and PNS

• This summary covers key concepts for the Unit 3 Theory Exam, with specific questions in the Weekly Lesson Activities.
• Each Unit-level outcome aligns with a Course Outcome.

Introduction to the Nervous System & Nervous Tissue

• The nervous system receives sensory information, processes information in the brain, and sends out motor commands to make responses

Central Nervous System (CNS) vs. Peripheral Nervous System (PNS)

• The CNS is the body's processing center while the PNS relays information from the CNS

Motor vs. Sensory Components

• The motor component controls movement by sending signals.
• The sensory component receives information from body receptors.

Somatic Motor vs. Autonomic Motor Divisions

• The somatic motor division controls voluntary skeletal muscle movements.
• The autonomic motor division controls involuntary functions like heart rate.

Neuron Components

• Key components include dendrites, soma, neuroglia, and axon.
• Dendrites receive signals, Axons output signals

Structural Types of Neurons

• Unipolar neurons are single-branched, found in afferent pathways, for sensory reception.
• Bipolar neurons have two branches, are found in sensory organs (eye and nose) and transmit sensory information to the CNS.
• Multipolar neurons have one axon and multiple branches. They are located in the brain and spinal cord CNS and control motor and sensory processing.

Functional Types of Neurons

• Three functional types – sensory, motor, and interneurons.
• sensory neurons transmit signals from the body to the CNS
• motor neurons transmit signals from the CNS to muscles/glands
• interneurons connect neurons within the CNS

Nervous System as a Control System

• This system receives information from sensory receptors, processes it in the CNS, and sends commands to effector organs to produce a response.
• It acts like a feedback loop to maintain homeostasis.

Neuroglial Cells (Glia)

• Glia are non-neuronal cells in the nervous system that support and protect neurons.
• Six types:
• astrocytes: star-shaped, CNS, support and regulate neuronal activity
• oligodendrocytes: CNS, form myelin
• microglia: CNS, immune cells
• ependymal cells: CNS, line ventricles and produce CSF
• Schwann cells: PNS, form myelin
• satellite cells: PNS, support and protect neurons

Myelination

• This is when glial cells (Schwann cells in the PNS and oligodendrocytes in the CNS) wrap their membranes around axons, forming a myelin sheath.
• This insulates and speeds up electrical signal transmission.

Ion Channels in Neurons

• Neurons possess four major types of ion channels: voltage-gated, ligand-gated, mechanically-gated, and leak channels
• Each plays a crucial role in neuronal signaling and located in specific regions of the neuron

Resting Membrane Potential (RMP)

• This is generated by K+ leaking from the inside of the cell to the outside via leak K+ channels, generating a negative charge inside the membrane.
• At rest, the membrane is impermeable to Na+, as all of the Na+ channels are closed.

Sodium-Potassium ATPase Pump

• The pump actively transports sodium ions out of the cell and potassium ions into the cell, against their concentration gradients, using energy from ATP hydrolysis.

Polarization Terminology

• Depolarization is a decrease by membrane potential
• Repolarization returns to resting potential
• Hyperpolarization is an increase in membrane potential
• Threshold represents the critical level needed to activate action potential

Graded Potentials vs. Action Potentials

• Graded potentials occur mainly in the dendrites and cell body, while action potentials propagate along the axon

Action Potential

• This is a rapid change in membrane voltage, initiated by a stimulus that depolarizes the cell, causing voltage-gated sodium channels to open, leading to sodium influx and further depolarization

Factors Affecting Conduction Velocity

• Larger axon diameters and myelination both contribute to faster conduction velocity

Refractory Periods

• Absolute refractory period is a time when no stimulus, regardless of strength, can trigger another action potential
• Relative refractory period follows and requires a stronger-than-usual stimulus to generate a new action potential

Chemical Synapse Structure

• A typical chemical synapse has:
• a presynaptic terminal containing neurotransmitter-filled vesicles
• a narrow synaptic cleft
• a postsynaptic membrane with receptors that bind to the released neurotransmitters

Synaptic Transmission

• Synaptic transmission occurs when an action potential reaches the axon terminal of a presynaptic neuron, causing calcium ions to influx
• This triggers the fusion of synaptic vesicles with the membrane
• Neurotransmitters are released into the synaptic cleft where they bind to receptors on the postsynaptic cell, producing an effect on the receiving neuron

Gray Matter vs White Matter

• Gray matter is primarily composed of neuron cell bodies, dendrites, and axon terminals
• White matter is mainly made up of myelinated axons

Nervous System Damage

• It can be damaged by
• Injury
• Infections
• Degeneration
• Structural defects
• Tumors
• Blood flow disruption
• Autoimmune disorders

Central Nervous System

• The meninges consist of three layers: the dura mater (outermost), arachnoid mater (middle), and pia mater (innermost)

Dural Venous Sinuses

• These are large, valveless venous channels within the dura mater, serving as the brain's primary venous drainage system
• Collect blood from cerebral veins and cerebrospinal fluid (CSF) from the subarachnoid space, then drain into the internal jugular vein

Cranial Dural Septa

• Formed by inward folds of the meningeal layer of the dura mater.
• Create partitions within the cranial cavity, separating different brain regions and limiting their movement.

Brain Spaces

• The epidural space is between the dura mater and the skull/vertebrae.
• The subdural space is between the dura and arachnoid mater.
• The subarachnoid space is between the arachnoid and pia mater and contains cerebrospinal fluid.

Cerebrospinal Fluid (CSF)

• It cushions for injury and provide nutrients
  • CSF is mostly produced by specialized ependymal cells in the choroid plexuses of the ventricles of the brain
  • Absorbed in the arachnoid granulations

Brain Terminology

• Gyrus: Ridge on the surface of the brain
• Sulcus: Shallow groove on cerebral cortex
• Fissure: A larger or deeper sulcus

Four Major Parts of the Adult Brain

• Cerebrum, Cerebellum, Brainstem, Diencephalon

Ventricular System Components

• Two lateral ventricles, one third ventricle, and one fourth ventricle (all connected by passageway filled with CSF)

Blood-Brain Barrier (BBB)

• Separates the brain from the bloodstream, shielding it from toxic substances

Cerebrum Landmarks

• Left and right hemispheres
• Four lobes
• Corpus callosum connects the two hemispheres

Three Major Cerebral Regions

• Cerebrum, Cerebellum, Brainstem

Cerebral Hemispheres

• It is divided into two hemispheres, each containing five lobes: frontal, parietal, temporal, occipital, and insula

Functional Cortical Areas

• Are organized into sensory, motor, and association areas

Cerebral White Matter Tracts

• Projection fibers connect the cortex to subcortical areas.
• Association fibers connect different cortical regions within the same hemisphere.
• Commissural fibers connect corresponding regions of the two hemispheres.

Diencephalon Components

• Thalamus, hypothalamus, posterior pituitary, epithalamus, pineal body, and subthalamus

Brainstem Subdivisions

• Midbrain (motor control, eye movements), pons (coordinates face and eye movements, hearing, balance), and medulla oblongata (regulates breathing, heartbeat, blood pressure)

Cerebellum

• Meaning "little brain" in Latin, is a brain structure situated at the back of the head, below the occipital and temporal lobes of the cerebrum and above the brainstem

Spinal Cord Functions

• Carrying messages between the brain and body, controlling movement, and regulating vital functions

Spinal Cord Anatomy

• It is a cylindrical structure that extends from the base of the skull through the vertebral canal.
• It divided into 31 segments with corresponding pairs of spinal nerves.
• Includes the cervical, thoracic, lumbar, and sacral enlargements.
• It ends at the conus medullaris with the nerve roots below forming the cauda equina.
• It is protected by the meninges and supplied by the anterior and posterior spinal arteries.

Spinal Cord Roots

• Anterior (ventral) roots carry motor (efferent) signals out of the spinal cord
• Posterior (dorsal) roots carry sensory (afferent) signals into the spinal cord

Spinal Cord Cross-Section

• Central, butterfly-shaped gray matter surrounded by white matter.
• Gray matter contains cell bodies, and white matter contains myelinated axons organized into tracts.

Spinal Cord Tracts

• Ascending tracts carry sensory information up to the brain
• Descending tracts transmit motor commands from the brain down to the spinal cord

Nervous System Changes

• Nervous system changes and consequences depend on the type of factor( ex: stress, injury, disease) and its potential impact on brain regions, neurotransmitters, and nervous system functions

Peripheral Nervous System

• Ganglia are synaptic relay stations between neurons

Nerve Microanatomy

• In a nerve's cross-section, individual axons are surrounded by endoneurium
• Grouped into fascicles encased in perineurium
• The entire nerve is enveloped by the epineurium, a dense connective tissue sheath.

Spinal Nerve Formation

• A spinal nerve, a mixed nerve formed by the union of dorsal (sensory) and ventral (motor) roots, emerges from the spinal cord through the intervertebral foramen and then splits into dorsal and ventral rami

Spinal Nerve Pairs

• There are 31 pairs of spinal nerves: 8 cervical (C1-C8), 12 thoracic (T1-T12), 5 lumbar (L1-L5), 5 sacral (S1-S5), and 1 coccygeal (Co)

Dermatome Definition

• It is a specific area of skin on the body that is primarily supplied by sensory nerve fibers from a single spinal nerve.
• It essentially acting like a "map" of the body's sensory innervation, allowing clinicians to identify potential nerve damage or spinal cord lesions based on the pattern of sensory loss in a particular dermatome area

Spinal Nerve Plexus definition

• It is a network of interweaving nerve fibers that arise from multiple spinal nerves.
• The cervical plexus supplies nerves to the posterior head and neck, as well as to the diaphragm.
• The brachial plexus supplies nerves to the arm.
• The lumbar plexus supplies nerves to the anterior leg.
• The sacral plexus supplies nerves to the posterior leg.

Somatic Nervous System (SNS) vs. Autonomic Nervous System (ANS)

• The Somatic Nervous System (SNS) controls voluntary movements of skeletal muscles through a single neuron pathway
• The Autonomic Nervous System (ANS) regulates involuntary functions like heart rate and digestion via a two-neuron pathway.

Nervous System Changes

• Nervous system changes and consequences depend on:
  • Injury
  • Infections
  • Degeneration
  • Structural defects
  • Tumors
  • Blood flow disruption
  • Autoimmune disorders

Sensory Receptors

• Sensory receptors are classified by the type of stimulus they respond to:
• chemoreceptors detect chemicals
• mechanoreceptors detect mechanical forces
• thermoreceptors detect temperature changes

General Sense vs Special Sense

• Special senses have specialized sense organs and include vision (eyes), hearing (ears), balance (ears), taste (tongue), and smell (nasal passages).
• General senses are all associated with touch and lack special sense organs
• touch receptors are found throughout the body, but particularly in the skin

Tactile Receptors

• Tactile receptors, or mechanoreceptors, are specialized nerve endings in the skin that detect touch, pressure, vibration, and texture
• They are different types located at varying depths and specialized for different stimuli

Tunics of the Eye

• The eye has
  • a fibrous tunic (sclera and cornea)
  • a vascular tunic (choroid, ciliary body, and iris)
  • a neural tunic (retina)

Cavities of the Eye

• The eye has two main fluid-filled cavities:
• the anterior cavity, located in front of the lens and divided into the anterior and posterior chambers.
• the posterior cavity (or vitreous chamber), behind the lens, filled with vitreous humor

Lens Function

• Focuses light rays onto the retina to help us see clearly

Extrinsic Eye Muscles

• Their function is to control movement

Accessory Eye Structures

• Eyelids, conjunctiva, and lacrimal (tear) glands

Rods vs. Cones

• Rods are for low light vision (black and white perception)
• Cones are for color vision and sharp detail

Visual Signal Pathway

• Visual signals originate in the retina, travel along the optic nerve, converge at the optic chiasm where some nerve fibers cross over, continue as the optic tract, and finally reach the brain's visual processing areas, including the lateral geniculate nucleus (LGN) and the visual cortex

Olfactory Epithelium

• The olfactory epithelium, responsible for detecting odors, is a specialized tissue located in the roof of the nasal cavity, composed of olfactory receptor neurons, supporting cells, and basal cells

Olfactory Receptor Activation

• Odorants activate olfactory receptors
• This Triggers a cascade that leads to the generation of an electrical signal
• Then the signal travels to the brain for odor perception

Olfactory Information Pathway

• Olfactory information travels from receptors in the nasal cavity, initiating action potentials in olfactory nerves, through the olfactory bulb, then via the olfactory tract to the olfactory cortex and other brain regions like the amygdala and hypothalamus

Taste Buds

• They are located on the tongue (they are little bumps called papillae)

Primary Taste Sensations

• Sweet(sugar, pleasurable), sour (acid), salty (sodium ions), bitter (harsh), unami (savory): tasted by tongue)

Taste Signal Pathway

• Taste information travels from gustatory receptors on the tongue via cranial nerves VII (facial), IX (glossopharyngeal), and X (vagus) to the nucleus of the solitary tract (NST) in the medulla, then to the thalamus, and finally to the gustatory cortex in the insula and frontal operculum for perception

The Ear

• The ear is divided into three sections: outer, middle, and inner
• Each has distinct structures and functions related to hearing and balance
• The outer ear collects sound waves, the middle ear amplifies and transmits them, and the inner ear converts them into nerve signals for the brain

Microscopic Structures of the inner ear

• The inner ear, housing structures for hearing and balance, contains the cochlea (for hearing), semicircular canals (for rotational motion), and the utricle and saccule (for linear motion and gravity sensing)

Sound Amplification

• Auditory canal to eardrum making vibrations. Vibrations amplified by auditory ossicles.

Generation of an Action Potential in the Spiral Organ

• Causes the hair cells to bend opening the ion channels which leads to depolarization and releases neurotransmitters.

Sound Signal Pathway

• Signals originate from the spiral organ (organ of Corti) in the cochlea, are transduced into electrical impulses that travel along the cochlear branch of the vestibulocochlear nerve (CN VIII) to the brainstem, ultimately reaching the auditory cortex in the temporal lobe

Equilibrium Receptor Cells

• Mechanoreceptors

Static vs. Dynamic Equilibrium

• Static items are at rest with zero net force. Dynamic items moving with constant velocity

Macula Structure

• Sensory epithelium containing hair cells that detect head position relative to gravity

Crista Ampullaris Structure

• The crista ampullaris, a sensory organ of rotation, is a cone-shaped structure within the ampulla of each semicircular canal which contains hair cells and a gelatinous cupula
• It detects angular acceleration and deceleration and is crucial for dynamic equilibrium

Vestibular Signal Pathway

• Signals from the maculae (utricle and saccule) and cristae ampullaris (in semicircular canals) travel via the vestibular branch of the vestibulocochlear nerve (CN VIII) to the vestibular nuclei in the brainstem and cerebellum, then to various brain areas for processing

Consequences of Nervous System Changes

• For example, the sympathetic nervous system can accelerate heart rate, widen bronchial passages, decrease motility (movement) of the large intestine, constrict blood vessels, cause pupil dilation, activate goose bumps, start sweating and raise blood pressure