Organization of the Nervous System

Flashcards covering the organization of the nervous system, including the central and peripheral nervous systems, spinal cord, brainstem, cerebrum, and related topics such as ascending/descending tracts, spinal reflexes, and the blood-brain barrier.

Peripheral Nervous System (PNS)

12 pairs of cranial nerves arising from the brainstem and above, and 31 pairs of spinal nerves arising from the spinal cord. Carries information between the CNS and the tissues of the body.

Afferent Division

Carries sensory information toward the CNS.

Efferent Division

Carries motor information away from the CNS toward the effector tissues (muscles and glands).

Spinal Cord Function

Processes reflexes; transmits nerve impulses to and from the brain; receives sensory input and initiates motor output.

Brainstem Function

Controls life-sustaining processes (e.g., respiration, circulation, digestion).

Cerebrum and Cerebral Cortex Function

Processes, integrates, and analyzes information; involved with highest levels of cognition, voluntary initiation of movement, sensory perception, and language.

Spinal Cord

Most anatomically inferior portion of the CNS; receives sensory input from the periphery of the body and contains cell bodies of motor neurons.

Ascending Pathways

Carry sensory input to higher levels of the CNS.

Descending Pathways

Carry impulses from the brain to motor neurons in the spinal cord.

Anatomical regions of the spinal cord

Cervical, thoracic, lumbar, and sacral.

Dorsal Root

Contains afferent, or sensory, neurons.

Ventral Root

Contains efferent, or motor, neurons.

Nerve

A bundle of neuronal axons found in the peripheral nervous system.

Tracts

Bundles of neurons with similar functions located within the CNS.

First-Order Sensory Neurons

Their cell bodies are found in the dorsal root ganglia, and they transmit impulses to higher levels of the CNS, alpha motor neurons, or interneurons.

Spinal Cord Gray Matter

Consists of nerve cell bodies and unmyelinated interneuron fibers and is divided into the dorsal, lateral, and ventral horns.

Spinal Cord White Matter

Consists of bundles of myelinated axons of neurons, or tracts.

Second-Order Sensory Neurons

Transmit nerve impulses to higher levels in the CNS and are found in the dorsal horn.

Somatic Motor Neurons

Their cell bodies are found in the ventral horn and exit the CNS through the ventral root of the spinal nerve to innervate skeletal muscles.

Alpha Motor Neurons

Innervate skeletal muscle fibres to cause contraction.

Gamma Motor Neurons

Innervate intrafusal fibers of the muscle spindle, which monitors muscle length.

Visceral Motor Neurons

Their cell bodies are found in the lateral horn, and their axons form efferent nerve fibers of the autonomic nervous system (ANS) to innervate cardiac muscle, smooth muscle, and glands.

Interneurons

These are found in all areas of the spinal cord gray matter and are responsible for the integrative functions of the spinal cord including reflexes.

Ventral Spinocerebellar Tract

A tract carrying information regarding unconscious muscle sense (proprioception) from the spinal cord to the cerebellum.

Ventral Corticospinal Tract

A tract carrying information regarding voluntary muscle control from the cerebral cortex to the spinal cord.

Descending Tracts

Terminate on and influence activity of alpha motor neurons in the ventral horn for voluntary movement of skeletal muscles.

Corticospinal (Pyramidal) Tracts

Originate in the cerebral cortex and descend directly to the alpha motor neurons in the spinal cord for fine, discrete, voluntary movements.

Multineuronal (Extrapyramidal) Tracts

Originate in the motor regions of the cerebral cortex, cerebellum, and basal ganglia and regulate overall body posture and subconscious movements.

Reflex

Occurs when a particular stimulus always elicits a particular response that is automatic and involuntary.

Components of a Reflex Arc

Sensory receptor, afferent neuron, integrating center in the spinal cord, efferent neuron, and effector tissue.

Withdrawal Reflex

Elicited by a painful or tissue-damaging stimulus to move the body part away from the stimulus.

Crossed-Extensor Reflex

Causes extensor muscles in the opposite limb to contract to provide support for the body during the withdrawal reflex.

Brainstem

Medulla, pons, and midbrain (mesencephalon). Receives sensory input and initiates motor output by way of cranial nerves III through XII.

CNI

Olfactory nerve (smell).

CN II

Optic nerve (vision).

CN III

Oculomotor nerve (eye, pupil, and lens movement).

CN IV

Trochlear nerve (rotates eye downward).

CN V

Trigeminal nerve (biting and chewing movements; sensory data from palate, teeth, gums, face, and cornea).

CN VI

Abducens nerve (lateral eye movement).

CN VII

Facial nerve (facial expressions, salivary gland secretion, taste sensation).

CN VIII

Vestibulocochlear nerve (hearing and balance).

CN IX

Glossopharyngeal nerve (speech, swallowing, salivation, blood pressure, blood gases, taste).

CN X

Vagus nerve (speech, swallowing, heart rate, stomach motility, abdominal and thoracic visceral sensation, blood pressure, blood gases, taste).

CN XI

Spinal accessory nerve (head movement).

CN XII

Hypoglossal nerve (tongue movement).

Medulla Function

Contains control centers for subconscious, involuntary functions, such as cardiovascular activity, respiration, swallowing, and vomiting.

Pons Function

Serves as a relay for the transfer of information between the cerebrum and the cerebellum and contributes to the control of breathing.

Midbrain Function

Controls eye movement and relays signals for auditory and visual reflexes; provides linkages between components of the motor system.

Reticular Formation

A diffuse network of neurons in the brainstem with a role in cortical alertness, ability to direct attention, and sleep.

Cerebrum and Cerebral Cortex

Most highly developed in humans and responsible for intellect, thought, personality, voluntary initiation of movement, final sensory perception, and language.

Cerebral Gray Matter

Contain the cell bodies of neurons and form the cerebral cortex.

Cerebral White Matter

Composed of the axons of neurons and is found underlying the cortex in the core of the cerebrum.

Types of Tracts in the Cerebrum

Projection, association, and commissural tracts.

Gyrus (pl. Gyri)

A convolution formed by the folds of the cerebral cortex.

Sulcus (pl. Sulci)

A shallow groove separating gyri.

Fissure

A deeper groove separating gyri.

Cerebral Lobes

Frontal, parietal, occipital, and temporal lobes.

Frontal Lobes Function

Responsible for voluntary motor activity, speaking ability, and higher intellectual activities.

Parietal Lobes Function

Process and integrate sensory information.

Occipital Lobes Function

Process mainly visual information.

Temporal Lobes Function

Process mainly auditory information.

Somatosensory Cortex

Located in the postcentral gyrus and contains the terminations of ascending pathways that transmit nerve impulses concerning temperature, touch, pressure, pain, and proprioception.

Proprioception

Awareness of posture, movement, changes in equilibrium, and the position of one’s body parts.

Unimodal Association Areas

Further integrates information from a single sensory modality and provides more complex aspects of the input.

Multimodal Association Areas

Integrate information about more than one sensory modality; the highest level of cognitive brain function takes place here.

Prefrontal Multimodal Association Area

Involved primarily with motor integration, long-term planning, personality traits, and behavior.

Posterior (Parieto-Occipito-Temporal) Association Area

Pools and integrates somatic, auditory, and visual stimuli for complex perceptual processing. Involved primarily with visuospatial localization, language, and attention.

Limbic Multimodal Association Area

Concerned with emotional expression and memory storage.

Motor Association Areas

Receive input from the basal ganglia, cerebellum, somatosensory cortex, etc.. programming complex sequences of movements and in orienting the body and limbs toward a specific target.

Primary Motor Cortex

Located in the precentral gyrus and initiates voluntary contractions of specific skeletal muscles.

Wernicke’s area and Broca’s area

These language skill cortical areas are found only in the left hemisphere.

Wernicke’s Area

Involved with language comprehension and is important for understanding spoken and written messages.

Broca’s Area

Responsible for the mechanical aspects of speaking.

Receptive Aphasia

Patient is unable to understand any spoken or visual information and speech, while fluent, is unintelligible.

Expressive Aphasia

Patient is able to understand spoken and written language but is unable to express his response in a normal manner. Speech is nonfluent and requires great effort because he cannot establish the proper motor command to articulate the desired words.

Basal Ganglia

Consist of four nuclei of gray matter embedded within the white matter of each cerebral hemisphere and contribute to the control of voluntary movement.

Thalamus

Located between the cerebrum and the brainstem and serves as a relay station for ascending tracts transmitting upward from the spinal cord, as well as sensory tracts from the eyes and the ears.

Hypothalamus

Lies beneath the thalamus and above the pituitary gland and plays an important role in regulating the autonomic nervous system and endocrine activity to maintain homeostasis.

Hypothalamus Function

Monitors sensory information, compares it to biological set points, and elicits autonomic, endocrine, and behavioral responses to reestablish homeostasis.

Cerebellum Function

Coordinates movement by evaluating differences between intended and actual movement.

Vestibulocerebellum Function

Controls axial muscles and limb extensors, assuring balance while standing still and during movement; controls eye movements.

Spinocerebellum Function

Influences muscle tone and coordinates skilled voluntary movements.

Cerebrocerebellum Function

Involved with the planning, programming, and initiation of voluntary activity and participates in procedural memories or motor learning.

Blood-Brain Barrier

Tight junctions fuse the endothelial cells together, and substance exchange between blood and the extracellular fluid of the brain is controlled by highly selective membrane-bound protein carriers.

Cerebrospinal Fluid (CSF)

Four ventricles or chambers form a continuous fluid-filled system composed of Cerebral Spinal Fluid mainly derived from the choroid plexuses of the two lateral ventricles.

Cerebrospinal Fluid (CSF) functions

protects the brain by serving as a shock-absorbing system between the brain and its bony capsule and facilitates its function of removing potentially harmful brain metabolites.