The Peripheral Nervous System

Flashcards covering the Peripheral Nervous System, cranial and spinal nerves, sensory receptors, dermatomes, and the autonomic nervous system divisions.

What are the two main functional divisions of the Peripheral Nervous System (PNS)?

The Somatic Nervous System and the Autonomic Nervous System.

What is the primary difference in function between the somatic and autonomic nervous systems?

The somatic nervous system connects the CNS to skeletal muscles and skin to oversee conscious activities, whereas the autonomic nervous system connects viscera to the CNS for involuntary control.

How are a nerve and a ganglion defined in the Peripheral Nervous System?

A nerve is a bundle of nerve fibers outside the CNS, while a ganglion is a cluster of neuron cell bodies outside the CNS.

What is the distinction between sensation and perception?

Sensation is the detection of stimuli (such as light, sound, or temperature), whereas perception is the brain's interpretation and understanding of those sensory inputs.

What is sensory adaptation?

Sensory adaptation is a process where sensory receptors become less responsive to constant or repetitive stimuli over time, allowing the nervous system to prioritize new or changing stimuli.

Which receptor type detects changes that deform the receptor structure?

Mechanoreceptors.

What is the function of chemoreceptors in the human body?

Chemoreceptors detect changes in the concentration of chemical substances, such as blood glucose levels or blood oxygen saturation.

What is the difference between simple receptors and complex receptors?

Simple receptors mediate general senses (such as Ruffini receptors in the skin), whereas complex receptors are dedicated to special senses (sight, hearing, smell, taste, and balance) and are confined to the head.

How does visceral pain differ from somatic pain, and what is referred pain?

Visceral pain originates in internal organs where receptors respond differently than surface receptors. Referred pain occurs when pain stimuli arising in viscera are perceived as somatic (surface) in origin.

What connective tissue layers wrap nerve components as shown in this diagram?

The endoneurium encloses individual axons and their myelin sheaths, the perineurium wraps fibers into bundles called fascicles, and the epineurium is the tough fibrous sheath enclosing the whole nerve.

Which cranial nerve is sensory for vision?

Cranial Nerve II (Optic nerve).

What are the primary functions of Cranial Nerve III (Oculomotor nerve)?

Motor fibers to eye muscles that raise the eyelid, direct the eyeball, constrict the iris (parasympathetic), and control lens shape.

Which cranial nerve provides motor innervation to the superior oblique muscle of the eye via a pulley system?

Cranial Nerve IV (Trochlear nerve).

What are the three divisions of Cranial Nerve V (Trigeminal nerve) and its main functions?

The three divisions are Ophthalmic, Maxillary, and Mandibular. It provides sensory information for the face and motor fibers to chewing muscles.

What function is carried out by Cranial Nerve VI (Abducens nerve)?

Motor fibers to the lateral rectus muscles of the eye.

What are the sensory and motor roles of Cranial Nerve VII (Facial nerve)?

Sensory function for taste, and motor fibers for facial expressions as well as lacrimal and salivary gland function.

Which cranial nerve carries sensory information for balance and hearing?

Cranial Nerve VIII (Vestibulocochlear nerve).

What are the sensory and motor functions of Cranial Nerve IX (Glossopharyngeal nerve)?

Sensory function for taste on the tongue and motor fibers to the throat.

Why is Cranial Nerve X called the Vagus or "wandering" nerve?

Because its sensory and motor fibers extend beyond the head and neck, supplying the pharynx, larynx, and continuing to viscera in the abdominal cavity.

Which muscles are innervated by Cranial Nerve XI (Accessory nerve)?

Motor fibers innervate muscles of the neck and upper back.

What is the main motor role of Cranial Nerve XII (Hypoglossal nerve)?

Motor fibers to the tongue for swallowing and speech.

Where are the sensory receptors and auditory cortex located for the sense of hearing?

Receptors are hair cells (mechanoreceptors) in the Organ of Corti inside the cochlea, and impulses are processed in the auditory cortex of the temporal lobe.

Which inner ear structures contain hair cells responsible for static balance and dynamic balance?

Maculae contain hair cells for static balance, and crista ampullaris contains hair cells for dynamic balance.

Where are olfactory receptors located, and to which brain area do they transmit sensory information?

Olfactory hairs (chemoreceptors) are in the olfactory epithelium of the nasal cavity, transmitting via the olfactory nerve to the primary olfactory area in the temporal lobe.

How many pairs of spinal nerves are present in the human body, and how are they divided by region?

There are 31 pairs total: 8 pairs of cervical, 12 pairs of thoracic, 5 pairs of lumbar, 5 pairs of sacral, and 1 pair of coccygeal nerves.

How do spinal nerves connect to the spinal cord and exit the vertebral column?

Spinal nerves connect via ventral (motor) and dorsal (sensory) roots, and exit through the intervertebral foramina.

What is a nerve plexus, and what benefit does it offer against spinal cord injury?

A nerve plexus is a nerve network originating from different spinal cord levels serving the same body part. It ensures that damage to a single spinal cord level is less likely to result in total paralysis of a muscle.

What is Hilton's law?

Hilton's law states that any nerve serving a muscle that moves a joint also innervates the joint and the skin over the joint.

What is a dermatome, and why does destruction of a single spinal nerve not produce complete numbness in that region?

A dermatome is the area of skin innervated by branches of a single spinal nerve. Because most dermatomes overlap, losing a single spinal nerve will not cause complete numbness.

What are the main structural and chemical differences between the somatic and autonomic motor pathways?

The somatic system uses single myelinated motor neurons releasing Acetylcholine (ACh) to stimulate skeletal muscle. The autonomic system uses two-neuron motor pathways innervating cardiac/smooth muscle and glands, releasing ACh, epinephrine, or norepinephrine for excitation or inhibition.

Where does the sympathetic nervous system originate, and what fiber length features characterize its neurons?

It originates from T1 to L2 (thoracolumbar region), featuring short preganglionic fibers with ganglia near the spinal cord and long postganglionic fibers.

What activities are represented by the "E division" of the sympathetic nervous system?

Exercise, excitement, emergency, and embarrassment.

Where does the parasympathetic nervous system originate, and what neurotransmitter does it always use?

It originates from the brain stem and S1–S4 (craniosacral region) and always uses Acetylcholine (ACh).

What activities are represented by the "D division" of the parasympathetic nervous system?

Digestion, defecation, and diuresis.

What contrasting effects do the sympathetic and parasympathetic divisions have on the heart?

The sympathetic division increases heart rate and force of heartbeat, whereas the parasympathetic division decreases heart rate, slowing and steadying it.

What contrasting effects do the sympathetic and parasympathetic divisions have on the lungs?

The sympathetic division dilates bronchioles, whereas the parasympathetic division constricts bronchioles.

How do the sympathetic and parasympathetic divisions affect the iris and ciliary muscles of the eye?

The sympathetic division dilates pupils and prepares the eye for distant vision. The parasympathetic division constricts pupils and increases bulging of the lens for close vision.

Which autonomic division stimulates sweat glands, arrector pili muscles, and the adrenal medulla?

The sympathetic division (the parasympathetic division has no effect on these targets).