Neurobiology Quiz: Neurons and Reflexes

Physiology & Pathophysiology MD 303

• This is a Level 2 clinical pharmacy program
• The nervous system is made up of billions of interconnected neurons in a highly organized circuit.
• The nervous system is divided into two major anatomically distinct regions: Central Nervous System (CNS) and Peripheral Nervous System (PNS).
• CNS includes the brain and spinal cord
• PNS includes 12 pairs of cranial nerves arising from the brainstem and 31 pairs of spinal nerves arising from the spinal cord.

The Nervous System

• Cranial nerves: Olfactory (smell), Optic (vision), Oculomotor (eye movement, pupil reflex), Trochlear (eye movement), Abducens (eye movement), Trigeminal (face sensation, chewing), Facial (face movement, taste), Vestibulocochlear (hearing, balance), Glossopharyngeal (throat sensation, taste, swallowing), Vagus (movement, sensation, abdominal organs), Accessory (neck movement), Hypoglossal (tongue movement).
• Each nerve has a specific function.

Spinal Cord

• The spinal cord is the most inferior portion of the CNS.
• It receives sensory input from the peripheral body and contains the cell bodies of motor neurons for voluntary and involuntary movements.
• The spinal cord processes sensory and motor activities in the trunk and limbs.
• Involuntary and simple reflexes are processed at the spinal cord level.
• Voluntary movements are initiated and controlled by thought processes in the cerebrum.

Levels of CNS Function

• The spinal cord processes reflexes and transmits nerve impulses to and from the brain, receives sensory input, and initiates motor output. It also controls life-sustaining processes.
• The Brain stem (consisting of medulla, pons, and midbrain) receives sensory input, initiates motor output, and is continuous with the spinal cord, controls subconscious, involuntary functions like cardiovascular activity, respiration, swallowing, and vomiting.
• The brainstem is a relay station for information transfer between the cerebrum and cerebellum, also aids in breathing. The midbrain controls eye movement, auditory, and visual reflexes.
• The cerebrum and cerebral cortex are responsible for processing, integrating, and analyzing information, involved with cognition, voluntary movement, sensory perception, and language.
• The cerebrum accounts for 80% of the total brain weight
• Voluntary movements are initiated in the cerebrum
• Convolutions increase surface area for more neurons
• The cerebral cortex processes information for intellect, thoughts, personality, sensory perception, voluntary movement initiation.

The Brain

• The brain is the integrative portion of the nervous system for receiving, processing, storing sensory information, and orchestrating motor response.
• The brain is divided into several distinct regions.
• The forebrain consists of the cerebrum, basal ganglia, thalamus, hypothalamus.
• Midbrain is part of the brainstem
• Hindbrain consists of pons, medulla, and cerebellum.

The Cerebrum

• The cerebrum is composed of two hemispheres.
• The hemispheres are connected to allow communication
• Gray matter (unmyelinated cell bodies) forms the cerebral cortex on the outer surface.
• White matter (myelinated axons) is within the core.
• Axons are bundled into tracts by function.

Nerves versus Tracts

• Nerves are bundles of axons found in the PNS only.
• Tracts are bundles of axons found in the CNS only.

Frontal Section of the Brain

• The cerebrum is made of white matter internally and gray matter externally forming the cerebral cortex.
• Basal ganglia and the thalamus are embedded within the cerebral hemispheres.
• The ventricles are filled with cerebrospinal fluid (CSF).

The Cerebral Cortex

• The cerebral cortex is folded, not smooth, increasing neuron space
• It's divided into four lobes: frontal, temporal, parietal, and occipital. Each lobe has a specific processing function.

The Basal Ganglia

• Masses of gray matter embedded in the white matter of each cerebral hemisphere.
• They contribute to voluntary movement control.

The Thalamus

• Located between the cerebrum and brainstem.
• Acts as a relay station for sensory input to the cerebral cortex (except olfactory).
• Acts as a filter for the cerebral cortex
• Involves the regulation of skeletal muscle contraction by positively reinforcing voluntary motor activity.

The Hypothalamus

• Lies beneath the thalamus.
• It plays a vital role in homeostasis.
• Its functions include regulating the autonomic nervous system, endocrine system, temperature, plasma volume, thirst, hunger, urine output, behavior, and emotions.

The Brainstem

• Consists of midbrain, pons, and medulla of the hindbrain.
• Contains control centers for subconscious, involuntary functions (cardiovascular, respiration, and swallowing)
• It acts as a relay station for information transfer between the cerebrum and cerebellum.
• It also plays a vital role in breathing, auditory, and visual reflexes.

The Reticular Formation

• A diffuse network of neurons in the brainstem.
• It plays key roles in cortical alertness, attention, sleep, emotional facial expressions, eating, breathing, and pain response.

The Cerebellum

• Part of the hindbrain
• Accounts for >50% of all brain neurons
• Important role in coordinating movement and maintaining balance and equilibrium.
• Plays a role when movements are in progress and during repetitions.

Cerebrospinal Fluid (CSF)

• Derived from the choroid plexus
• CSF composition differs from plasma composition.
• The CSF maintains a consistent chemical environment for neurons, which optimizes function.
• Serves as a protective shock absorber.
• Constant turnover facilitates removal of harmful metabolites

The Spinal Cord

• Lowest level of the CNS.
• Divided into cervical, thoracic, lumbar, sacral, and coccygeal regions, each subdivided into functional segments.
• A pair of spinal nerves extend from each segment.

Functional Types of Neurons in the Spinal Cord

• Second-order sensory neurons (dorsal horn): receive input from afferent neurons.
• Visceral motor neurons (lateral horn): related to the autonomic nervous system (ANS).
• Somatic motor neurons (ventral horn): innervate skeletal muscles.
• Interneurons (throughout gray matter): small, unmyelinated, receive input from higher CNS levels and sensory neurons to perform integrative functions like reflexes.

Spinal Reflexes

• Reflexes are categorized based on the effector (skeletal muscle, smooth muscle, glands) and region of the CNS processing the reflex (cranial or spinal).
• Simple (preprogrammed) reflexes, and acquired (learned) reflexes
• Reflex arcs involve sensory receptors, afferent neurons, integrating centers in the spinal cord, efferent neurons, and effector tissues which produce a reflex response.
• Monosynaptic vs. polysynaptic reflexes

Test your knowledge on the types of neurons, their functions, and the role of the spinal cord in reflex actions. This quiz covers essential concepts related to the nervous system and its anatomical divisions. Understand how sensory information is processed and transmitted within the human body.