Nervous System Overview Quiz

Nervous System Overview

• The nervous system has a functional organization with basic divisions, including the spinal cord and meninges.
• The system encompasses sensory, motor, behavioral, and higher cognitive functions.
• Cognitive functions involve memory, thinking, reasoning, understanding, judgment, and behavior.

Function of the Nervous System

• Sensory input monitors changes (stimuli) inside and outside the body.
• Integration processes and interprets sensory input and determines the appropriate response.
• Motor output activates muscles or glands to cause the effect.

Nervous System Divisions

• The central nervous system (CNS) includes the brain and spinal cord acting as the processing center. It receives input from the periphery.
• The peripheral nervous system (PNS) connects the CNS to the periphery, transmitting information to and from the CNS. Somatic and autonomic divisions exist in the PNS.
• The somatic nervous system controls voluntary movements of skeletal muscles.
• The autonomic nervous system controls involuntary actions of smooth muscles, cardiac muscles, and glands.

Functional Classification of Neurons

• Sensory (afferent) neurons transmit nerve impulses from sensory receptors (both somatic and visceral types.)
• Motor (efferent) neurons convey nerve impulses from the central nervous system (CNS) to muscles and glands.
• Somatic motor neurons control voluntary skeletal muscle contractions.
• Autonomic motor neurons regulate smooth muscle, cardiac muscle, and gland activity.
• Interneurons connect sensory and motor neurons within the CNS.

Spinal Cord Structure

• The spinal cord finishes growing by age 4, while the vertebral column finishes growing between ages 14 and 18.
• In adults, the spinal cord occupies only the upper 2/3 of the vertebral column.
• The spinal cord is typically longer in males (approximately 45 cm) than in females (approximately 42 cm).
• The spinal cord has margins including the foramen magnum, L1/L2 vertebra and the conus medullaris.
• The cauda equina is a collection of nerve roots at the inferior end of the vertebral canal.
• Two enlargements of the spinal cord exist at the cervical (C5 to T1) and lumbosacral (L1 to S3) levels for upper and lower limbs, respectively.

Spinal Meninges

• The dura mater extends to the posterior surface of vertebral body S2.
• The subdural space is between the dura and arachnoid mater.
• The arachnoid mater is the middle meningeal layer.
• The subarachnoid space is located deep to the arachnoid mater.
• The pia mater is the innermost layer adhering to the surface of the spinal cord.

Spinal Cord Features

• The spinal cord is attached laterally to the dura by denticulate ligaments.
• These ligaments are continuous flat sheets of connective tissue.
• The anterior median fissure and posterior median sulcus are prominent features.
• The spinal cord contains gray matter, which is butterfly-shaped and central within the cord.
• The spinal cord's white matter surrounds the gray matter and contains ascending (sensory) and descending (motor) pathways.

Spinal Cord Nuclei

• Spinal neurons are organized into nuclei and Rexed lamina (10 zones.)
• Neuronal cells are grouped based on their structure and function.

Spinal Cord White Matter

• White matter within the spinal cord is made up of axons that connect the brain to the body.

Spinal Cord Blood Supply

• Anterior spinal artery supplies the anterior 2/3 of the spinal cord.
• Two posterior spinal arteries supply the posterior 1/3 of the spinal cord.

Spinal Cord Blood Supply

• Arterial vasocorona is an anastomosis between the spinal arteries.
• This vasocorona system supplies the pia mater.

Spinal Blood Supply

• Arteries come from vertebral and radicular arteries supplying various parts of the spinal cord.

Spinal Blood Vessels

• Anterior and posterior spinal veins are present, draining into radicular veins.
• Vertebral venous plexuses (internal and external) receive drainage from radicular veins that eventually empty into vertebral segmental veins.

Spinal Cord Functions

• Conduction: input and output along the spinal cord.
• Neural Integration: receiving multiple inputs, integrating, and producing appropriate outputs.
• Locomotion: coordinated muscle contractions, such as walking.
• Reflexes: involuntary reactions to stimuli important for posture and coordination.

Reflexes

• Reflexes are quick, involuntary, and stereotyped reactions to stimuli of glands or muscles.
• A reflex arc includes sensory input, sensory neuron activation, information processing in the CNS, motor neuron activation, and a peripheral effector response. Reflex arcs involve pathways that include sensory and motor structures in the CNS and PNS.

Reflex Arc

• Five main steps involved in a simple reflex: the arrival of a stimulus and receptor activation, sensory neuron activation, information processing in the CNS, motor neuron activation, and response by a peripheral effector.

Reflex Arc Components

• Afferent nerve fibers carry information from somatic receptors to spinal cord.
• Integrating centers are neuronal contact points in gray matter within the spinal cord or brainstem.
• Efferent nerve fibers carry motor impulses to effectors (muscles).

Nervous System Aging

• Gray matter increases until age 8-10 and then decreases after, though some increases occur later in density.
• White matter loss by volume averages 28% from age 20 to 90.
• Reduction of gray matter in neocortex averages 12% from ages 20 to 90.