Chapter 8 : Nervous System

Joel G. Soria, MD

Sensory input Integration Homeostasis Mental activity Control of muscles and glands

Functions of the Nervous System

• Central nervous system (CNS) • Brain and Spinal Cord

• Peripheral nervous system (PNS) • Sensory divisions • Motor divisions

• Somatic motor nervous system • Autonomic nervous system (ANS)

Division of Nervous System

NEURON

AXONDENDRITES

MYELIN SHEATH NODES OF

RANVIER

NUCLEUS

AXON HILLOCK

CELL BODY

1. Neurons

2. Microglia

Astrocytes

Ependymal cells

Microglia

Oligodendrocytes

Schwann cells

Cells of the NERVOUS SYSTEM

3. Myelin sheaths

4. Organization of Nervous Tissue

A. Grey matter

B. White matter

Types of Neuron

MULTIPOLAR

BIPOLAR

UNIPOLARMany dendrites, single axon Most motor and CNS neurons

single dendrites, single axon

Special sense organs

Single process Most sensory neurons

Types of MICROGLIA

ASTROCYTES

EPENDYMAL CELLS

MICROGLIAL CELLS

OLIGODENDROCYTE

SCHAWNN CELLS

Schwann Cells

Organization of Nervous Tissue

Gray Matter

non-myeline sheath Brain – Cortex; PNS - Ganglion

White MatterMyelined sheath CNS – conduction pathways, nerve tracts

conduction in an

unmyelinated sheath

conduction in a myelinated sheath

REFLEX – involuntary reaction in response to a stimulus applied to the periphery and transmitted to the CNS. Allows the person to move quickly REFLEC ARC – Neuronal pathway in which the reflex occurs Basic foundation unit the nervous system

REFLEXES

5 Basic components

Convergent and divergent pathway

Convergent and divergent pathway

SPINAL CORD

Extends from the foramen magnum to the 2nd lumbar vertebrae

Cauda equina

SPINAL CORD

STRETCH REFLEX

• Simplest form of reflex • Muscle contracts in response to a

stretching force applied to them • Knee-jerk reflex / patellar reflex

WITHDRAWAL REFLEX

• Remove a limb or body part from a painful stimulus

• Usually involves flexor muscle groups

Spinal Nerves

• Arise along the lateral side of the vertebra

• Formed by the union of the dorsal and ventral roots

• All spinal nerves are mixed (both sensory and motor) in function

• Most of the spinal nerves are organized in groups “PLEXUSES” 1. Cervical plexus 2. Brachial plexus 3. Lumbosacral plexus

Cervical plexus

• Arises from spinal nerves C1-C4

• Innervates several muscles on the neck.

• Innervates the PHRENIC NERVE

Brachial plexus

• Arises from spinal nerves C5-T1 • Forms 5 major Nerve of the Upper

Extremities • Axillary nerve – Shoulder muscles • Radial nerve – All muscles of the

posterior arm and forearm • Musculocutaneous Nerve–

Anterior muscles of the arm • Ulnar nerve – 2 forearm muscles

and the intrinsic muscle of the hand • Median nerve – Muscles of the

anterior forearm

Lumbosacral Plexus

• Arises from spinal nerves L1-S4 • OBTURATOR NERVE – innervate

the muscles of the inner thigh and skin

• FEMORAL NERVE –muscles of the Anterior thigh and skin (+ skin of medial side of the leg)

• TIBIAL NERVE – Posterior thigh muscles, anterior and posterior leg muscles, and most of intrinsic foot muscles.

• COMMON FIBULAR NERVE – innervate the muscles of the inner thigh and skin

• SCIATIC NERVE – conbination of common fibular and tibial nerve

B R A I N

Brainstem

Connects spinal cord to the brain Consist of: Medulla oblongata Pons Midbrain

Functions vital functions: Control of heart rate, blood pressure and breathing

Medulla Oblongata

Most inferior part of the brainstem Contains ascending and descending Pyramids- descending tracts Conscious control of skeletal muscle

Functions as: Regulation of heart rate, blood vessel diameter, breathing, swallowing, vomiting, coughing, sneezing, balance, and coordination.

Pons

Contains ascending and descending tracts Relay information between cerebrum and cerebellum. Footbridge

Functions as: Breathing, swallowing, balance, and control. Chewing and salivation.

Midbrain

Smallest region of the brainstem Colliculi – 4 mounds posterior to the midbrain

2 inferior – major relay centers for auditory nerve pathways 2 superior – Visual reflexes; turning the head on a tap shoulder, sudden noise, bright flash of light

Coordination of eye movements and in diameter of pupil and lens shape. Substancia nigra – basal nuclei

Regulation of general body movement

Reticular formation

Scattered throughout the brainstem Regulating cyclical motor functions such as respiration, walking, and chewing. RAS (Reticular Activating System) – Arousing and maintaining consciousness and in regulating sleep-wake cycle.

Diencephalon

Largest part of diencephalon Influences mood and registers unlocalized, uncomfortable perception of pain.

Thalamus

Small area located superior-posterior to the thalamus Emotional and visceral response to odors

Epithalamus

Most inferior part of the diencephalon Maintaining homeostasis Control of body temperature, hunger, and thirst

Hypothalamus

Sexual pleasure, feeling of good after a meal, rage, and fear. Infundibulum – funnel-shaped stalk Major role in controlling hormones from the pituitary gland

Ascending Tracts

Homunculus