Nervous System Overview

Components of a Reflex Arc

• The five components are receptors, sensory neuron, interneuron, motor neuron, and effector
• Receptors receive stimuli
• Sensory neurons transmit afferent signals
• The integration center processes information
• Motor neurons send efferent signals
• Effectors initiate a response

General Functions of the Nervous System

• The nervous system collects information
• The nervous system processes and evaluates information
• The nervous system initiates responses

Divisions of the Nervous System

• The central nervous system includes the brain and spinal cord
• The peripheral nervous system includes nerves and ganglia
• The sensory nervous system detects stimuli and transmits information to the CNS
• The motor nervous system initiates and transmits information from the CNS to effectors
• The somatic sensory system receives sensory input from the five senses and proprioceptors
• The visceral sensory system receives sensory input from internal organs
• The somatic motor system controls skeletal muscle
• The autonomic motor system controls cardiac muscle, smooth muscle, and glands

Afferent vs. Efferent Division of PNS

• The afferent division transmits sensory information to the CNS
• The efferent division transmits motor commands from the CNS to effectors
• Another name for afferent is sensory, and another name for efferent is motor

Somatic vs. Autonomic Nervous System

• The somatic nervous system controls voluntary movements like muscle contractions
• The autonomic nervous system regulates involuntary bodily functions like heart rate, digestion, and breathing

Primary Functions of the Motor Division

• The motor division transmits nerve impulses from the central nervous system to muscles and glands

Visceral Definition

• Visceral relates to both sensory and motor functions
• Visceral carries sensory information to the internal organs to the central nervous system

General Structural and Functional Characteristics of Neurons

• Neurons consist of a cell body (soma), dendrites, and an axon

Neuron Structure

• The cell body houses the nucleus and other organelles
• Dendrites receive signals from other neurons
• The axon transmits signals to other neurons or effectors
• The axon hillock initiates action potentials
• Myelin sheath insulates the axon
• Nodes of Ranvier are gaps in the myelin sheath that speed up signal transmission
• Synaptic end bulbs release neurotransmitters to communicate with other cells

Perikaryon of a Neuron

• The perikaryon is the cell body, also called the soma

Unipolar, Bipolar, and Multipolar Neurons

• Multipolar neurons are the most common type
• Unipolar neurons have one process extending from the cell body
• Bipolar neurons have two processes (one axon and one dendrite)
• Multipolar neurons have one axon and multiple dendrites

Interneurons

• Interneurons are located exclusively within the central nervous system (brain and spinal cord)

Mixed Nerve

• it contains both sensory and motor fibers

Synapse

• The places where neurons connect and communicate with each other
• Synapses are formed when the axon terminal of one neuron comes into close contact with the dendrites or cell body of another neuron

Electrical Synapses

• Electrical synapses are coupled directly through gap junctions
• They allow ions to flow directly between pre- and postsynaptic neurons

Neurons vs. Glial Cells

• Neurons are the functional units of the nervous system, gathering and transmitting electrical impulses
• Glial cells are supporting cells that provide structure, nourishment, and protection to neurons

Types of Glial Cells and Their Functions

• Astrocytes maintain the brain environment by regulating neurotransmitters, ions, and blood flow
• Oligodendrocytes form the myelin sheath around axons in the central nervous system
• Microglia play a crucial role in brain repair and defense

Nerve

• A nerve is a bundle of nerve fibers (axons) held together by connective tissue
• The three layers of connective tissue:
  • Endoneurium
  • Perineurium
  • Epineurium

Lobes of the Cerebrum

• The lobes are named frontal, parietal, temporal, and occipital

Gyri and Sulci

• Gyri are the raised ridges on the cerebral cortex
• Sulci are the indentations or grooves between those ridges

White and Gray Matter

• Gray matter consists of neuron cell bodies and dendrites
  • In the cerebrum, it is located in the outer cortex
  • In the spinal cord, it forms the central "butterfly" shape surrounded by white matter on the outside
• White matter consists of myelinated axons
  • In the cerebrum, it is found deeper inside

Cranial Meninges

• Dura mater (outer layer)
• Arachnoid mater (middle layer)
• Pia mater (inner layer)

Ventricles in the Brain

• Lateral ventricles: located in the left and right hemispheres
• Third ventricle: located in the diencephalon of the forebrain
• Fourth ventricle: located in the back of the pons and upper half of the medulla oblongata of the hindbrain

Cerebrospinal Fluid (CSF)

• CSF is a clear, watery liquid produced in the ventricles of the brain by the choroid plexus
• CSF circulates around the brain and spinal cord as a protective cushion, providing nutrients, and removing waste products

Blood-Brain Barrier

• Tightly packed endothelial cells lining the blood vessels in the brain

Cerebral Cortices

• Frontal lobe (front of the brain)
• Parietal lobe (top of the brain)
• Temporal lobe (side of the head)
• Occipital lobe (back of the head)
• Insular cortex (deep inside the brain, underneath the frontal, parietal, and temporal lobes)

Functions of Cerebral Hemispheres

• The left cerebral hemisphere controls language processing, logic, analytical thinking, and mathematical abilities
• The right cerebral hemisphere controls spatial reasoning, creativity, emotional processing, and holistic perception

Decussation

• It involves the crossing over of nerve fibers from one side of the CNS to the opposite side, forming an X-like pattern

Components of the Diencephalon

• Thalamus relays sensory information to the cerebral cortex
• Hypothalamus maintains homeostasis by controlling vital functions and regulating the endocrine system
• Epithalamus regulates circadian rhythms through melatonin production
• Subthalamus coordinates movements by sending signals to the substantia nigra

Cerebral Peduncles

• Two stalks connect the cerebrum to the brainstem, located in the midbrain

Cerebellum

• Located at the back of the head and is responsible for coordinating movement, balance, and posture

Connection to the Brainstem

• The cerebellum is connected through three pairs of nerve bundles called "cerebellar peduncles"

Limbic System

• Network of brain structures responsible for processing emotions, motivation, and memory
• Hippocampus is control center for memory formation, particularly consolidating short-term memories into long-term storage

Reticular Formation

• The reticular formation involves sensory and motor functions and is responsible for activation

Cranial Nerves and Their Functions

• Olfactory nerve: sense of smell
• Optic nerve: vision
• Oculomotor nerve: eye movement and pupil control
• Trochlear nerve: eye movement (downward and inward gaze)
• Trigeminal nerve: facial sensation and chewing
• Abducens nerve: lateral eye movement
• Facial nerve: facial expressions and taste on the anterior tongue
• Vestibulocochlear: hearing and balance
• Glossopharyngeal: taste on the posterior tongue, swallowing, and saliva production
• Vagus nerve: autonomic functions like digestion, heart rate, and breathing
• Accessory nerve: neck muscle movement
• Hypoglossal nerve: tongue movement

Primary Segments of the Spinal Cord

• The segments are cervical, thoracic, lumbar, sacral, and coccygeal

Length of Adult Spinal Cord

• The adult spinal cord is around 45 centimeters (18 inches) and is not the same length as the vertebral canal

Spinal Cord Anchored to Coccyx

• The spinal cord is anchored by the filum terminale

Pairs of Spinal Nerves

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

Spinal Nerves

• Most spinal nerves are mixed

Meninges of the Spinal Cord

• The meninges: dura mater, arachnoid, and pia mater
• Cerebrospinal fluid (CSF) is located in the subarachnoid space between the arachnoid and pia mater

Posterior and Lateral Horns of the Spinal Cord

• Posterior horn: sensory processing, receiving incoming sensory information
• Lateral horn: involved in the autonomic nervous system, particularly the sympathetic division

Spinal Cord Communication

• Gray matter serves as communication between the left and right sides of the spinal cord

Conduction Pathway

• Is a network of specialized muscle cells within the heart that initiates and transmits electrical impulses;
• Consists of sinoatrial(SA) node, atrioventricular(AV) node, bundle of Hls, bundle branches, and purkinje fibers

Rami

• Rami(ramus) refers to a branch of a spinal nerve
• The anterior ramus goes towards the front of the body
• The posterior ramus goes towards the back of the body

Plexus

• It is a network fo nerves or bloode vessels that branch out and reconnect; located in many body parts, including the neck, shoulders, back, and pelvis

Dermatomes

• It is a specific area of skin on the body that is primarily supplied by sensory nerve fibers form a single spinal nerve
• They are useful by allowing healthcare providers to pinpoint the location of nerve damage to spinal cord lesions based on patterns of sensory loss in specific dermatomal areas

Dorsal and Ventral Root

• Dorsal root carries sensory information towards the central nervous system and contains the cell bodies, within called the dorsal root ganglion
• Ventral root carries motor information away from the CNS, with the cell bodies of motor neurons located within the spinal cord itself