Nervous System Overview Quiz

Nervous System Overview

• The nervous system controls rapid bodily activities.
• It gathers and processes information from sensory organs to initiate a response.

Intended Learning Outcomes

• Outline the classification of the nervous system.
• Recognize the anatomical organization of the nervous system.
• Identify the major levels of central nervous system (CNS) functions.
• Understand different types of sensations.
• Identify parts of the motor nervous system and identify lesions.
• Define synapse and identify its functional anatomy across different junctions.
• Recognize the sequence of neurotransmitter release at synaptic junctions.

Organization of the Nervous System

• The nervous system is divided into central and peripheral systems.
• The central nervous system (CNS) includes the brain and spinal cord.
• The peripheral nervous system (PNS) encompasses nerves transmitting signals to and from the CNS.

Anatomical Organization of the Nervous System (CNS)

• The CNS, including brain and spinal cord, is housed within the skull and vertebral column.
• The PNS is comprised of nerves that extend between the CNS and peripheral tissues.
• The PNS consists of cranial nerves (12 pairs) originating from the brain and spinal nerves (31 pairs) from the spinal cord.
• Individual PNS fibers are extensions of sensory or motor neurons.

Central Nervous System: Brain

• The brain is divided into four main parts: cerebrum, diencephalon, brainstem, and cerebellum.
• Cerebral ventricles are interconnected cavities filled with cerebrospinal fluid (CSF).

Cerebrum: Two Cerebral Hemispheres

• The cerebrum's surface is convoluted, consisting of gyri and sulci.
• The cerebral cortex, a thin outer layer of gray matter, comprises neuron cell bodies.
• White matter, beneath the cortex, is a thick core formed of myelinated axons.
• The corpus callosum connects the right and left cerebral hemispheres.
• Each hemisphere is divided into four lobes: frontal, parietal, occipital, and temporal.
• Lobes contain specific areas for functions like visual, auditory, and sensory processing.

Cerebrospinal Fluid (CSF)

• CSF is secreted by choroid plexuses in the walls of cerebral ventricles.
• The total volume of CSF is roughly 150 mL.
• CSF turnover is approximately 500 mL per day.
• CSF acts as a cushion for the brain, preventing injury to delicate nervous tissue.

Increased Intracranial Pressure (IICP)

• Normal IICP ranges from 5-15 mmHg.
• IICP can result from tumor growth, edema, excess CSF, or hemorrhage.
• Clinical hallmarks include headache, vomiting, and papilledema (optic disc swelling).

Blood Supply to the Brain

• The brain requires a substantial blood supply (15-20% of total cardiac output) due to its high metabolic rate.
• The blood-brain barrier separates circulating blood from brain tissue, and plays a role in drug design.
• The Circle of Willis is a circulatory anastomosis supplying blood to the brain.

Structure of Neurons

• Neurons exhibit diverse shapes and sizes but generally possess a cell body (soma), dendrites, an axon, and axon terminals.
• Dendrites receive input, the axon transmits impulses away from the soma, and axon terminals release neurotransmitters.

Synapses

• Synapses are the junctions between neurons.
• Chemical synapses are the predominant type, relying on neurotransmitter release.
• Electrical synapses involve electrical coupling via gap junctions.

Action of Neurotransmitters

• Released neurotransmitters diffuse across the synaptic cleft.
• They bind to specific receptor proteins.
• Neurotransmitter action can be excitatory or inhibitory.

Major Levels of CNS Functions

• The cerebrum and cerebral cortex are the highest functional levels, processing and analyzing information.
• The brainstem controls life-sustaining functions and relays sensory input and motor output.
• The spinal cord processes reflexes and transmits signals between the brain and the body.

Sensory Nervous System

• The sensory nervous system carries information about the external and internal environment to the CNS.
• It gathers sensory input, integrates it, and transmits it to the CNS and eventually to motor systems. Sensory pathways involve three types of neurons: first-order, second-order, and third-order neurons.

Sensations

• The main function of the sensory system is to detect changes in both the internal and external environment.
• This includes general sensation (like pain, temperature, pressure), special sensations (vision, hearing, taste, smell) , and organic sensations (hunger, thirst).

Pain Sensation

• Pain is a common sensation, warning of potential tissue damage.
• Nociceptors are pain-sensitive nerve endings activated by various stimuli.
• Pain can be classified into several types, including cutaneous, deep, and visceral pain.

Peripheral Neuropathy

• Peripheral neuropathy is a general term encompassing diseases affecting peripheral nerves, causing motor, sensory, or autonomic dysfunction.

Motor Nervous System

• The motor nervous system sends commands from the CNS to muscles and glands, enabling voluntary movement, coordination of movement.
• It includes upper motor neurons (UMNs) and lower motor neurons (LMNs).

Motor Reflexes

• Reflexes are involuntary responses to stimuli.
• The monosynaptic reflex (e.g., muscle stretch reflex) involves a simple pathway with one synapse.
• The polysynaptic reflex (e.g., flexor withdrawal reflex, crossed extensor reflex) involves more complex pathways with multiple synapses.

Upper and Lower Motor Neurons

• Upper motor neurons originate in the brain and activate lower motor neurons.
• Lower motor neurons project from the spinal cord to muscles and glands.

Motor Lesions

• Damage to upper motor neurons (UMNs) typically results in weakness or paralysis in the body's opposite side and hyperreflexia or spasticity.
• Damage to lower motor neurons (LMNs) results in weakness or paralysis affecting the same side of the body and hyporeflexia.

The Cerebellum

• The cerebellum is crucial for coordinating voluntary movements, maintaining muscle tone, and equilibrium.
• Cerebellar damage can lead to problems with incoordination and balance.

The Basal Ganglia

• The basal ganglia are essential for regulating muscle tone, initiating voluntary movements, and controlling automatic movement.
• Dysfunction of the basal ganglia produces motor problems like slow movements, tremors, and rigidity.

Let's Think Together

• Chemical synapses are the most prevalent synapse type in humans.

Additional Note

• Afferent nerves send information to the central nervous system (CNS), while efferent nerves send information from the CNS.