Stanbridge - T1 - Physiology - W5 - Peripheral NS, Autonomic NS, and Special Senses

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Questions and Answers

Which function is primarily associated with the oculomotor nerve (CN III)?

Taste sensation from the anterior tongue

Motor control of eye muscles and pupil constriction (correct)

Sensory function for the cornea

Visual acuity

What is the main role of the trigeminal nerve (CN V)?

Drives heart rate and gastrointestinal tract function

Serves as the primary sensory nerve for the face (correct)

Controls muscles of facial expression

Responsible for balance and hearing

Which reflex is primarily responsible for maintaining posture and balance during a loss of balance?

Stretch reflex

Tendon reflex

Crossed-extensor reflex (correct)

Pupillary reflex

What distinguishes the sympathetic nervous system from the parasympathetic nervous system?

Sympathetic fibers involve the fight-or-flight response Signup and view all the answers

Which cranial nerve is primarily responsible for balance and hearing?

Vestibulocochlear nerve (CN VIII) Signup and view all the answers

Which cranial nerve is responsible for the innervation of the lateral rectus muscle of the eye?

Abducens nerve (CN VI) Signup and view all the answers

What is the main integration center of the autonomic nervous system (ANS)?

Hypothalamus Signup and view all the answers

What are the special senses listed in the content?

Vision, Hearing, Taste, and Smell Signup and view all the answers

Which muscle of the eye is innervated by both the oculomotor nerve and the trochlear nerve?

Inferior oblique muscle Signup and view all the answers

What is the primary function of cranial nerves related to special senses?

Transmission of sensory information Signup and view all the answers

How do the sympathetic and parasympathetic nervous systems typically function?

They continuously adjust to maintain homeostasis. Signup and view all the answers

In terms of visual pathways, how is the eye's visual information processed?

Through the thalamus before reaching the cortex Signup and view all the answers

Which of the following statements about chemical senses is accurate?

Chemicals must dissolve in liquid to be detected by taste receptors. Signup and view all the answers

Which type of sensory receptor responds to muscle stretch and initiates a reflex causing contraction?

Muscle spindles Signup and view all the answers

What is the primary function of joint kinesthetic receptors?

Provide information on joint position and motion Signup and view all the answers

Visceral pain is often misinterpreted as somatic pain due to what phenomenon?

Referred pain Signup and view all the answers

Which structure within peripheral nerves carries sensory information towards the central nervous system?

Sensory nerves Signup and view all the answers

What type of receptors are primarily responsible for responding to painful stimuli and tissue damage?

Nociceptors Signup and view all the answers

Which of the following statements is true regarding the regeneration of peripheral nerves?

If the cell body is intact, PNS axons can regenerate. Signup and view all the answers

What type of corpuscle is responsible for sensing deep pressure and vibrations?

Pacinian corpuscles Signup and view all the answers

Which of these receptors are grouped under proprioceptors?

Muscle spindles Signup and view all the answers

What do encapsulated nerve endings primarily function as?

Mechanoreceptors Signup and view all the answers

What type of sensory receptor is most common and largest in number in the body?

General senses Signup and view all the answers

Which type of sensory receptor responds specifically to temperature changes?

Thermoreceptors Signup and view all the answers

What function do exteroceptors primarily serve?

Detect stimuli outside of the body Signup and view all the answers

What is the primary role of nociceptors?

Detect potentially damaging stimuli Signup and view all the answers

Which of the following cranial nerves is responsible for the sense of smell?

Olfactory nerve Signup and view all the answers

What is Wallerian degeneration?

A process occurring after nerve injury Signup and view all the answers

What characterizes chemoresponders?

They respond to changes in blood chemistry Signup and view all the answers

Which of the following best describes photoreceptors?

Respond to light Signup and view all the answers

Identify the function of interoceptors.

Respond to stimuli from inside the body Signup and view all the answers

Which cranial nerve is primarily involved in taste sensation?

Facial nerve Signup and view all the answers

What is the primary pathway for visual information from the eye to the brain?

Optic pathway Signup and view all the answers

What is the primary function of the saccule in the vestibular system?

Respond to linear acceleration and vertical movement Signup and view all the answers

Which structure in the inner ear is involved in detecting head tilt and horizontal movement?

Utricle Signup and view all the answers

How does the endolymph in the semicircular canals contribute to balance?

It bends the cupula, stimulating hair cells Signup and view all the answers

What is the role of olfactory cilia in the process of smell?

To increase surface area for odorant detection Signup and view all the answers

Which cranial nerve is primarily responsible for transmitting olfactory signals?

Olfactory nerve (CN I) Signup and view all the answers

Where do the olfactory nerves synapse after projecting through the ethmoid bone?

Olfactory bulbs Signup and view all the answers

What is the relationship between the semicircular canals and the vestibular nerve?

Semicircular canals respond to head rotation, activating the vestibular nerve Signup and view all the answers

What role does mucus play in the function of the olfactory receptors?

It traps odorants for detection by olfactory sensory neurons Signup and view all the answers

Which part of the semicircular canals detects head tilt to the side?

Posterior canal Signup and view all the answers

What happens to signals from the olfactory bulbs after they synapse with mitral cells?

Signals are refined and sent to the olfactory cortex Signup and view all the answers

Study Notes

Peripheral Nervous System (PNS) and Autonomic Nervous System (ANS)

The PNS is part of the nervous system outside the central nervous system (CNS)
The CNS contains the brain and spinal cord
The PNS includes cranial and spinal nerves connecting to sensory and motor organs
The ANS is a subdivision of the PNS that regulates involuntary actions, such as heart rate and digestion

PNS Objectives

List the components
List the types of receptors
Understand nerve axon regeneration
Define Wallerian degeneration
List cranial nerves and functions
Describe how peripheral nerves exit the spinal cord
Understand reflex arcs

Classification of Sensory Receptors by Stimulus Type

Mechanoreceptors: respond to mechanical force (touch, pressure, stretch, vibration, and blood pressure)
Thermoreceptors: respond to temperature changes
Photoreceptors: respond to light (in the eyes)
Chemoreceptors: respond to chemicals in solution (smell, taste, blood chemistry)
Nociceptors: respond to potentially damaging stimuli (pain, extreme temperatures, pressure, inflammation)

Classification of Sensory Receptors by Location

Exteroceptors: located on or near body surfaces; respond to stimuli from the external environment (touch, pressure, pain, temperature, special senses)
Interoceptors (visceroceptors): located in internal organs and blood vessels; respond to stimuli within the body (chemical changes, stretch, temperature)
Proprioceptors: located in tendons, joints, ligaments, connective tissue; respond to internal stimuli (stretch and position)

Classification of Sensory Receptors by Structure

General senses: most common; modified dendritic endings of sensory nerves, encapsulated and non-encapsulated.
Special senses: located in special sensory organs

Simple Receptors of the General Senses: Non-Encapsulated/Free Nerve Endings

Located almost everywhere in the body
Mostly located in epithelium and connective tissue
Respond to painful stimuli; changes in temperature; some respond to tissue movements by pressure or itch
Hot or cold outside normal thermoreceptor range activates nociceptors (pain)
Epithelial tactile complexes (Merkel cells and discs): response to light pressure
Hair follicle receptors: respond to bends in hair

Simple Receptors of the General Senses: Encapsulated Nerve Endings

One or more sensory neuron fiber terminals enclosed in a connective tissue capsule; usually mechanoreceptors
Tactile corpuscles (Meissner's corpuscles): few sensory terminals, located in hairless skin; sense light touch
Lamellar corpuscles (Pacinian corpuscles): detect deep pressure or vibrations; best at vibration or 'on/off' stimulus
Bulbous corpuscles (Ruffini endings): detect deep continuous pressure; located in dermis, subcutaneous tissue, and joint capsules (like tendon organs)
Muscle spindles: proprioceptors in perimysium (around fascicles); detect muscle stretch
Tendon organs: proprioceptors in tendons close to skeletal muscle; detect tendon stretch

Simple Receptors of the General Senses: Encapsulated Nerve Endings: Types

Joint kinesthetic receptors: proprioceptors that monitor stretch in the capsules around synovial joints; contain lamellar and bulbous corpuscles, free nerve endings, similar to tendon organs; provide information about joint position and motion

Neural Integration in Sensory Systems: Sensation and Perception

Processing of sensory information at multiple levels (perceptual, circuit, and receptor levels)
Processing of sensory information in the brain
Processing of sensory input from different body parts

Pain Perception

All people share the same pain threshold.
Pain tolerance varies considerably between individuals.
Visceral pain travels the same pathways as somatic pain.
Referred pain occurs when pain stimuli is in one location, but felt in another.

Structure of a Nerve

Bundles of axons, connective tissue wrappings, myelin, blood vessels, and lymphatic vessels make up peripheral nerves
Sensory nerves carry information to the CNS.
Motor Nerves carry information away from the CNS.
Mixed nerves contain both

Ganglia versus Nuclei

Nuclei: collections of neuron cell bodies in the CNS.
Ganglia: collections of neuron cell bodies in the PNS (e.g., associated with the PNS) ; afferent nerve (sensory) fiber ganglia; efferent nerve (motor) fiber ganglia (usually from the autonomic nervous system)

Regeneration of Nerves

Mature neurons do not divide.
If a neuron's cell body is damaged, the axons of peripheral nerves can regenerate.
If a neuron cell body is not damaged, other neurons may die as well if the signals are severed.
Regeneration is limited by distance and tissues blocking further growth (PNS only)

Why can't CNS axons regenerate?

CNS axons generally do not regenerate after injury
Oligodendrocytes produce growth-inhibiting proteins that stop axon growth.
Astrocytes at the injury site form scar tissue that blocks further growth

Regeneration of axons in the PNS

Neuronal cell body has rough endoplasmic reticulum break apart and the cell body swells
Axons regenerate at 1.0mm per day
The longer the distance between the injury, the less likely the regeneration
Other tissues block the growth

Regeneration of a peripheral nerve fiber

The injured part of the nerve fiber degenerates.
The proximal portion of the nerve fiber begins to grow
New nerve connections are made

Spinal Nerves

31 pairs of spinal nerves
Branches from the spinal cord that innervate the body and form parts of the PNS
Carry sensory information to the CNS and motor information from the CNS
Form plexuses (bundles of nerves) in specific regions (cervical, brachial, lumbar, sacral)

Spinal nerves - anatomical specifics

Exit positions relative to the vertebra are important anatomic details

Nerves from the spinal cord

Dorsal and ventral rootlets attach to the length of the spinal cord segments and then form dorsal and ventral roots.
Ventral roots contain motor/efferent fibers; dorsal roots contain sensory/afferent fibers.
Roots unite to form spinal nerves just distal to the dorsal root ganglia.
Spinal nerves exit through the intervertebral foramina
Dorsal rami supply posterior body; ventral rami supply rest of the trunk and limbs

Nerves forming a plexus

Dorsal and ventral rami from the spinal nerve form a plexus.
This is a complex interwoven network of nerves

Tiny meningeal branches

Enter the vertebral column to innervate the meninges and vascular structures of the canal

Stretch Reflex

Response that contracts a muscle in response to stretch
Sensory receptors (muscle spindles) detect stretch and trigger a reflex signal.
This signal travels to the spinal cord where it activates motor neurons.
These motor neurons stimulate the muscle to contract, opposing the stretch

Golgi Tendon Organ

Response that relaxes a muscle in response to tension
Sensory receptors (Golgi tendon organs) detect the tension in the tendons that attach to the muscle.
They trigger a reflex signal to the spinal cord.
The signal inhibits the motor neurons that innervate the muscle, relaxing it.

The Tendon Reflex

Involves simultaneous contraction of a muscle and relaxation of its antagonist.
It acts as a safety mechanism to prevent damage to muscles and tendons during excessive force.
This mechanism allows the body to maintain balance and coordination during movement

The Crossed-Extensor Reflex

An automatic response from a withdrawal reflex in one limb; results in automatic extension of the opposite limb, or support, to maintain balance.
Triggered by pain or a noxious stimulus on one limb
Involves a crossed pathway within the spinal cord inhibition of the flexors (withdrawal) and activation of extensors (support) in the opposite limb

Cranial Nerves

12 pairs of cranial nerves;
Most serve only the head and neck but the vagus (CN X) innervates structures within the abdomen
Some cranial nerves (sensory and motor), others both sensory and motor
First two (I & II) attach to the forebrain (other nerves come from the brain stem)

Cranial Nerves (Table)

The document provides details about each cranial nerve: location, sensory and/or motor functions, and parasympathetic (PS) fibers (if applicable)

Cranial Nerves – Basic Functions

Summary of the sensory and motor functions, and areas innervated by each of the 12 cranial nerves;

Autonomic Nervous System (ANS)

Regulates organs and glands via involuntary actions.
Preganglionic neuron connects spinal cord/brainstem to ganglion
Postganglionic neuron connects to an effector

Effectors of the Somatic and Autonomic Pathways

Effector organs- skeletal muscles (somatic) & Cardiac muscle, smooth muscle, glands (autonomic)

Sympathetic versus Parasympathetic Nervous System

Sympathetic (fight or flight): increases HR, BP, dilates pupils, constricts lungs.
Parasympathetic (rest and digest/rest and repair): slows HR, BP, constricts pupils, relaxes lungs.

Differences between the Sympathetic and Parasympathetic Nervous Systems

Sites of origin: Sympathetic - thoracic and lumbar spinal cord; parasympathetic - brain stem and sacral spinal cord
Length of fibers: Sympathetic - short preganglionic, long postganglionic; parasympathetic - long preganglionic, short postganglionic
Location of ganglia: Sympathetic - close to the spinal cord; parasympathetic - within or near the effector organs

Parasympathetic Nervous System (diagram)

Shows the origin, path of preganglionic and postganglionic fibers and ganglia for the parasympathetic nervous system

Sympathetic Nervous System (diagram)

Shows the origin, path of preganglionic and postganglionic fibers and ganglia for the sympathetic nervous system

Autonomic Nervous System

Hypothalamus is the main integrating center
The brain stem has the most direct control
Overlap between somatic and autonomic systems exists in function
Rare all-or-none responses; they usually in homeostasis, fine adjustments only

Special Senses

Main special senses: vision, hearing, balance, taste, and smell;

Special Senses Objectives

Describe functions
Describe pathways
Identify cranial nerves

The Eye and Visual Sense

Extrinsic muscles: Superior, Inferior, Medial, Lateral rectus, and Superior and Inferior oblique–these are muscles that move the eye in all directions and are controlled by specific cranial nerves

Structure of the Eyeball

Fibrous outer layer components: sclera (white part of the eye), cornea (transparent part of the eye)
Vascular layer; Choroid, Ciliary body, Iris (includes the pupil)
Inner layer (Retina): location of processing; photoreceptors (rods and cones); blood vessels. Optic disc
The process of vision: light enters eye, travels through the optical system and focuses on the retina. Transmission to the optic pathways in the brain.

Hearing and Ear Anatomy

Outer ear: pinna (auricle), external acoustic meatus (auditory canal)
Middle ear: tympanic membrane (eardrum), ossicles (malleus, incus, stapes), auditory (Eustachian) tube
Inner ear: cochlea (hearing), semicircular canals (balance)

Hearing and Balance

External ear (hearing-sound collection)
Middle ear (hearing-sound transfer/amplification)
Inner ear (hearing-sound detection; balance-balance detection / maintain body position )

Cochlea

Bony chamber that contains the cochlear duct and the Organ of Corti
Cochlea has three chambers

The Process of Hearing

Sound waves enter the outer ear, travel through the ear canal, and vibrate the tympanic membrane.
The vibrations are transferred to the ossicles (small bones).
These bones transmit vibrations to the oval window in the inner ear.
Vibrations within the cochlea activate hair cells in the Organ of Corti.
The signal travels to the auditory brainstem and then to the auditory cortex.

Balance (Inner Ear)

Vestibule (saccule and utricle): respond to linear acceleration and head position
Semicircular canals: respond to rotational movements of the head

Balance and Equilibrium Transmission to the Brain and Reflexes

Input from vestibular receptors, visual receptors, and somatic receptors
Central nervous system processing areas (vestibular nuclei in brain stem, cerebellum)
Output to oculomotor control, spinal motor control (muscles for eyes, neck, limbs, and trunk)

Chemical Senses: Smell (Olfaction)

Air enters nasal cavity to the olfactory receptors.
Olfactory sensory neurons and cilia in the nasal conchae (superior nasal cavity).
Cilia increase surface area for odorant detection.
Mucus traps odorants.
Olfactory nerve (CN I) projects to the olfactory bulbs

Chemical Senses: Taste (Gustatory Sense)

Taste buds contain gustatory receptor cells.
Receptor hairs contact with chemicals in the saliva
Sensory dendrites surround each cell
Receptor cells release neurotransmitters (NT) /ATP as NT, triggering action potential which is then relayed to the brain

Taste Process

Taste sensations occur when chemicals are dissolved in saliva
Molecules contact gustatory hairs
Depolarization, causing action potential release of a neurotransmitter

Taste Process (continued)

Anterior 2/3rds of the tongue: cranial nerve VII (facial nerve)
Posterior tongue and pharynx: cranial nerve IX (glossopharyngeal)
Epiglottis & lower pharynx: cranial nerve X (vagus nerve)
Synapses in the medulla, relaying signals to the brain and then to the gustatory cortex in the insula.
Pathways also project to hypothalamus and limbic systems.

Taste affected by:

Smell accounts for 80% of taste.
Mouth temperature, other receptors, also affect perception.

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