CHAPTER 12 : Integration of Nervous System Functions

Chapter 14 - Integration of Nervous System Functions

Integration of Nervous System Functions - Sensation

Senses: Means by which brain receives information about environment and body

General: Distributed over large part of body

Somatic: Touch, pressure, temperature, proprioception, pain

Visceral: Internal organs and consist mostly of pain and pressure

Special senses: Smell, taste, sight, hearing, balance

Sensation or perception: Conscious awareness of stimuli received by sensory receptors

Types of Sensory Receptors

Mechanoreceptors: Compression, bending, stretching of cells

Chemoreceptors: Smell and taste

Thermoreceptors: Temperature

Photoreceptors: Light as vision

Nociceptors: Pain

GENERAL CLASSIFICATION:

Exteroreceptors: Associated with skin

Visceroreceptors: Associated with organs

Proprioceptors: Associated with joints, tendons

Sensory Nerve Endings

Free nerve endings: Cold receptors and warm

Merkels disk: Light touch, superficial pressure

Hair follicle receptor: Light touch, bending of hair

Pacinian corpuscle: Deep cutaneous pressure, vibration and proprioception

Meissners corpuscle: Two-point discrimination

Ruffinis end organ: Continuous touch or pressure

Muscle spindle: Proprioception as to muscle stretch and control of muscle tone

Golgi tendon organ: Important in muscle contraction and tendon stretch proprioception

Responses of Sensory Receptors

Receptor: Interaction of stimulus with sensory receptor produces a local potential

Primary: Have axons that conduct action potential in response to receptor potential

Secondary: Have no axons and receptor potentials produced do not result in action potentials but cause release of neurotransmitters

Accommodation or adaptation: Decreased sensitivity to a continued stimulus

Proprioceptors

Tonic: Example is know where little finger is without looking

Phasic: Example is you know where hand is as it moves

Sensory Nerve Tracts

Transmit action potentials from periphery to brain

Each pathway involved with specific modalities

First half of word indicates origin, second half indicates termination

Three Ascending Pathways

The specific and nonspecific ascending pathways send impulses to the sensory cortex

These pathways are responsible for discriminative touch and conscious proprioception

The spinocerebellar tracts send impulses to the cerebellum and do not contribute to sensory perception

Spinothalamic System

Conveys cutaneous sensory information to brain

Unable to localize source of stimulus

Divisions

Lateral for pain and temperature

Anterior for light touch, pressure, tickle, itch

Dorsal-Column/Medial-Lemniscal System

 Carries sensations of

Two-point discrimination

Proprioception

Pressure

Vibration

  

Tracts

Fasciculus gracilis

Fasciculus cuneatus

Spinocerebellar System

Carry proprioceptive information to cerebellum

Actual movements can be monitored and compared to cerebral information representing intended movement

Tracts

Posterior

Anterior

Lateralization of Cortical Function

Lateralization - each hemisphere has abilities not shared with its partner

Cerebral dominance - designates the hemisphere dominant for language

Left hemisphere - controls language, math, and logic

Right hemisphere - controls visual-spatial skills, emotion, and artistic skills

Major Lobes, Gyri, and Sulci of the Cerebral Hemisphere

Deep sulci divide the hemispheres into five lobes:

Frontal, parietal, temporal, occipital, and insula

Central sulcus - separates the frontal and parietal lobes

Lateral sulcus - separates the parietal and temporal lobes

The precentral and postcentral gyri border the central sulcus

Cerebral Cortex

It enables sensation, communication, memory, understanding, and voluntary movements

Each hemisphere acts contralaterally (controls the opposite side of the body)

No functional area acts alone; conscious behavior involves the entire cortex

Functional Areas of the Cerebral Cortex

Three types of functional areas are:

Motor areas : control voluntary movement

Sensory areas : conscious awareness of sensation

Association areas : integrate diverse information

Primary Somatosensory Cortex

Located in the postcentral gyrus, this area:

Receives information from the skin and skeletal muscles

Exhibits spatial discrimination

Somatosensory homunculus  caricature of relative amounts of cortical tissue devoted to each sensory function

Primary Motor Cortex

Located in the precentral gyrus

Composed of pyramidal cells whose axons make up the corticospinal tracts

Allows conscious control of precise, skilled, voluntary movements

Motor homunculus  caricature of relative amounts of cortical tissue devoted to each motor function

Brocas Area

Brocas area

Located anterior to the inferior region of the premotor area

Present in one hemisphere (usually the left)

A motor speech area that directs muscles of the tongue

Is active as one prepares to speak

Descending Motor Pathways

Descending tracts deliver efferent impulses from the brain to the spinal cord, and are divided into two groups:

Direct pathways equivalent to the pyramidal tracts

Indirect pathways, essentially all others

Motor pathways involve two neurons (upper and lower)

Descending Spinal Pathways

Direct

Control muscle tone and conscious skilled movements

Direct synapse of upper motor neurons of cerebral cortex with lower motor neurons in brainstem or spinal cord

Tracts

Corticospinal

Lateral

Anterior

The Direct (Pyramidal) System

Direct pathways originate with the pyramidal neurons in the precentral gyri

Impulses are sent through the corticospinal tracts and synapse in the anterior horn

Stimulation of anterior horn neurons activates skeletal muscles

Parts of the direct pathway innervate cranial nerve nuclei

The direct pathway regulates fast and fine (skilled) movements

Descending Spinal Pathways

Indirect

Synapse in some intermediate nucleus rather than directly with lower motor neurons

Tracts

Rubrospinal

Reticulospinal

Indirect (Extrapyramidal) System

Includes the brain stem, motor nuclei, and all motor pathways not part of the pyramidal system

These motor pathways are complex and multisynaptic, and regulate:

Axial muscles that maintain balance and posture

Muscles controlling coarse movement of the proximal portions of limbs

Head, neck, and eye movement

Reticular nuclei � maintain posture

Vestibular nuclei � receive input from the equilibrium apparatus of the ear and cerebellum

Vestibulospinal tracts � control the segmental apparatus during standing

Red nuclei � control flexor muscles

Speech

Speech area normally in left cerebral cortex

Wernicke�s area: Sensory speech

Brocas area: Motor speech

Aphasia: Absent or defective speech or language comprehension

Types of Sleep

There are two major types of sleep:

Non-rapid eye movement (NREM)

Rapid eye movement (REM)

 One passes through four stages of NREM during the first 30-45 minutes of sleep

 REM sleep occurs after the fourth NREM stage has been achieved

Types and Stages of Sleep: NREM

NREM stages include:

Stage 1 : eyes are closed and relaxation begins; one can be easily aroused

Stage 2 : irregular with sleep spindles (high-voltage wave bursts); arousal is more difficult

Stage 3 : sleep deepens; vital signs decline; dreaming is common

Stage 4 : skeletal muscles are relaxed; arousal is difficult

Types and Stages of Sleep: REM

REM sleep is characterized by

EEG pattern reverts through the NREM stages to the stage 1 pattern

Vital signs increase

Skeletal muscles (except ocular muscles) are inhibited

Most dreaming takes place

Sleep Patterns

Alternating cycles of sleep and wakefulness reflect a natural circadian rhythm

Although RAS activity declines in sleep, sleep is more than turning off RAS

The brain is actively guided into sleep

Nuclei of the hypothalamus regulate the sleep cycle

A typical sleep pattern alternates between REM and NREM sleep

Importance of Sleep

Slow-wave sleep is presumed to be the restorative stage

Those deprived of REM sleep become moody and depressed

REM sleep may be a reverse learning process where superfluous information is purged from the brain

Daily sleep requirements decline with age

Sleep Disorders

Narcolepsy - lapsing abruptly into sleep from the awake state

Insomnia - chronic inability to obtain the amount or quality of sleep needed

Sleep apnea - temporary cessation of breathing during sleep

Memory

Sensory

Very short-term retention of sensory input

Short-term - Information retained for few seconds to minutes

Long-term -

Explicit or declarative

Retention of facts

Accessed by hippocampus and amygdaloid (emotional)

Implicit or procedural

Development of skills as riding a bicycle

Memory is the storage and retrieval of information

The three principles of memory are:

Storage : occurs in stages and is continually changing

Processing :  accomplished by the hippocampus and surrounding structures

Memory traces :  chemical or structural changes that encode memory

Stages of Memory

The two stages of memory are short-term memory and long-term memory

Short-term memory (STM, or working memory)  a fleeting memory of the events that continually happen

STM lasts seconds to hours and is limited to 7 or 8 pieces of information

Long-term memory (LTM) has limitless capacity

Transfer from STM to LTM

Factors that affect transfer of memory from STM to LTM include:

Emotional state : we learn best when we are alert, motivated, and aroused

Rehearsal : repeating or rehearsing material enhances memory

Association : associating new information with old memories in LTM enhances memory

Automatic memory : subconscious information stored in LTM

Pain

Types

Referred: Sensation in one region of body that is not source of stimulus

(This may be due to the fact that visceral pain afferents travel along the same pathways as somatic pain fibers)

Phantom: Occurs in people who have appendage amputated or structure removed as tooth

Chronic: Not a response to immediate direct tissue injury

Effects of Aging on Nervous System

Gradual decline in sensory and motor function

Reflexes slow

Size and weight of brain decrease

Decreased short-term memory in most people

Long-term memory unaffected or improved

General CNS Disorders

Infections

Encephalitis: Inflammation of the brain

Rabies: Viral disease transmitted by bite of infected animal

Multiple sclerosis: Possibly involves autoimmune response to viral infection

Other disorders

Stroke: CVA or cerebrovascular accident caused by hemorrhage, thrombosis, embolism

Aneurysm: Dilation or ballooning of an artery

Alzheimers disease: Severe type of dementia

Epilepsy: Group of brain disorders that have seizures

Spinal Cord Trauma: Transection

Cross sectioning of the spinal cord at any level results in total motor and sensory loss in regions inferior to the cut

Paraplegia - transection between T1 and L1

Quadriplegia - transection in the cervical region

Amyotrophic Lateral Sclerosis (ALS)

Lou Gehrigs disease - neuromuscular condition involving destruction of anterior horn motor neurons and fibers of the pyramidal tract

Symptoms - loss of the ability to speak, swallow, and breathe

Death occurs within five years

Linked to malfunctioning genes for glutamate transporter and/or superoxide dismutase

PNS Disorders

General disorders

Anesthesia: Loss of sensation

Hyperesthesia: Increased sensitivity to pain, pressure, light

Paresthesia: Tingling, prickling, burning

Neuralgia: Nerve inflammation causing stabbing pain

Sciatica: Pain radiating down back of thigh and leg

 

Infections

Herpes: Skin lesions

Shingles or herpes zoster: Adult disease of chickenpox

Poliomyelitis: Infantile paralysis

Genetic and autoimmune disorders

Myasthenia gravis: Results in fatigue and muscular weakness due to inadequate ACh receptors

Nervous System Integration

I. Ascending Pathways to Brain

a.Neuronal Composition of the Sensory Pathway to the Brain

b.The Main Ascending Pathways

c.Nonspecific Ascending Pathways

d.Specific ascending pathways

II. Descending Pathways to Brain

a.       Pyramidal

b.       Extrapyramidal

III. Sleep

a.       REM

b.       NREM

IV. Memory

V.  Spinal Cord Trauma and Disorders

1. Spinal Cord Trauma

a. Paralysis

b. Paresthesias

c. Transections of the Cord

2. Poliomyelitis

3. Amyotrophic Lateral Sclerosis