Physiology Unit 5 Nervous System

Nervous System P 1+2,

Afferent Neurons

Carry information to the CNS

Sensory (ascending) tracts

• carry information up from the spinal cord up to the brain

Motor (descending) tracts

• Carry info from the brain down to the spinal cord to lower motor neurons

Efferent Neurons

Carry info away from CNS

Association (inter-) neurons

carry info within the CNS

Sensory Pathways

• form peripheral receptors to the primary sensory cortex of the cerebrum

• Consist of 3 neurons

1st Order Sensory Neuron

• Afferent Neuron

• Cell body in Dorsal root

• Carries impulses from receptors in skin, joints, and muscles to the spinal cord or brainstem

2nd order sensory neuron

• Cell body in the grey matter of the spinal cord or brain stem

• Carries impulses to the thalamus

3rd order sensory neuron

• Cell boidy in thalamus

• Carries impulses sto thhe primary sensory area of the cerebral corthex

Spinal Cord

• Gray matter is divided into horns

• White matter is divided into columns (funiculi)

Spinocerebrellar Tracts loaction

• Some cross in spinal cord

• Ascend contralaterally or ipsilaterally

• end at the cerebellum

Spinocerebellar Tracts Function

• Unconscious proprioception/

• Maintaining posture/Balance

• Co-ordination of complex movements

Anterior Spinocerebellar Tracts Loaction

• Cross in spinal cord

• ascend contralaterally

• End at the cerebellum

Posterior Spinocerebellar Tract Location

• Dont cross in spinal cord

• Ascend ipsilaterally

• end at the cerebellum

Posterior + Anterior Spinocerebellar tract

• Located in funiculi

• Both sides of cerebellum receive info from both sides of the body

Dorsal Columns Location

• located in dorsal funiculus

• ascend ipsilaterally to medulla

• cross at the medulla

• end at the thalamus

Dorsal Column Functions

• Transmit info from receptors in skin, muscles, and joints

• Transmit sensations:

• pressure

• Fine touch

• Body sense

• Stereognosis

• Vibration

Spinothalmic Tracts location

• Cross in spinal cord

• ascend contralaterally

• end at the thalamus

Lateral Spinothalamic Tracts Functions

• Sense Pain

• Sense Temp

Anterior Spinothalmic Tracts Function

• Crude touch

• itch, tickle

• presure from bowels, bladder

• sexual sensation

Thalamus

• Forms lateral walls of the third walls of the third ventricle

• Sensory relay center

• Contains cell bodies of 3rd order sensory neurons

Reticular Activating System (RAS)

• Diffuse network of brainstem neurons

• regulates level of alertness/consciousness

• Acsending impulses pass through otw to the thalamus

• Pain signals entering this system = Strong arousal throughout the brain

Hemispheric Laterality

Left and right hemispheres are not equal

Cerebral Dominance

• Hemisphere which contains the general interpretive and speech

• 90% of the pop the left hemisphere dominates language

• Governs mathematical abilities and logical reasoning

Non-Dominant hemisphere

Right hemi dominates:

• Art + Music enjoyment

• Spatial and pattern perception

• Recognition of emotion in language

• Generation of mental images of senses

Right Dominance

• 10% of ppl

• Usually Left-handed male

Co-Dominance

1-3% of ppl neither hemi dominates

• May be ambidexterous or dyslexic

The Hemispheres

• In continuous communication via corpus callosum

• Emotional (right) hemi permits fantasizing and sponatneous behaviour

• Logical (left) hemi inhibits rash emotional displays

Frontal Lobe

• Vouluntary control of movement

• “Higher” mental processes

Motor areas of Frontal Lobe

• Primary motor area

• premotor area

• broca’s area

• prefrontal area

• Olfactory area

Primary Motor area

• pre-central gyrus

• Controls voluntary movement of skeletal muscle

• Amount of cortex devoted to various body parts is proportional to the precision of motor control

• Larger amount devoted to face and hands

Pre motor area

• Anterior to primary motor area

• Controls learned, repetitive, motor skills

Broca’s area

• Frontal lobe, near lateral fissure

• predominantly in left hemi

• motor speech area

Prefrontal area

• Anterior region of frontal lobe

• Molded by experience

prefrontal area responsibilities

• Formation of abstract ideas

• conscience

• judgement

• motivation

• intelligence

• personality

Olfactory area

• medial surface of temporal lone, inferior surface of frontal lobe

• receives input from olfactory receptors

Primary sensory area

• Somatosensory Cortex

• Post-central gyrus

• Receives sensory input from receptors in skin

• Input from proprioceptors in muscles

Cortical distribution of primary sensory function

• larger amount devoted to face and hands

Proportional to their sensitivity

Somatosensory association area

• Posterior to primary sensory area

• interprets sensory input

Gustatory area

• in the tongue area of somatonsensory cortex

• receives input from the

Temporal Lobe Motor areas

• Primary auditory area

• auditory association area

• Wernickle’s area

• Affective language area

Primary Auditory area

receives impulses from the cochlea

Auditory Association Area

interprets whether sound is noise, speech, or music

Wenicke’s area

• In left hemi

• Necessary for comprehension of written and spoken language

Affective language Area

• Usually in left hemi in regions corresponding to broca’s and wernickles areas

• verbal expression of emotions

• detection of emotional content of words

Aphasia

• Loss of the ability to produce or comprehend words

• Non-Fluent = Difficulty in finding the right word

• Fluent = Can speak words but doesn’t make sense

Occipital lobe motor areas

• Primary visual area

• visual association area

Primary Visual area

• receives input from the retina via the thalamus

Visual association areas

• adjacent to to primary visual area

Cerebral Tracts

• Transmit signals between different parts of the cerebrum + lower brain centres + spinal cord

• White matter is mostly fond in the interior of the cerebrum

3 Cerebral Tracts

• Commissural Tracts

• Projection Tracts

• Association Tracts

Commissural Tracts

• Connect corresponding regions of the hemispheres, through the corpus callosum

Projection Tracts

• Afferent fibres up to cerebral cortex

• Efferent fibres down from cortex

Association tracts

Connect different regions within a hemisphere

Grey matter of the crebrum

• Site of higher brain function

• Cerebral Cortex

• Limbc system

• Basal ganglia

Cerebral cortex

• Outer layer of the cerebrum

• Only a few mm thick

• Neurons arranged in anatomically distinct vertical columns and layers

• High brain functions arise within these layers of the cerebral cortex

Limbic System

• Most primitive region

• Connects higher congnitve functions (emotions, reasoning etc)

• Plays a role in memory storage + Retrieval

• Controls aspects of involuntary behaviour

• Concerned with motivation, emotion, and memory

Basal ganglia (basal Nuclei)

• Receive input form entire cerebral cortex

• Involved in controlling movement + Cognition

• controls gross + automatic movements (eg swinging arms)

• Inhibit muscle tone in body

Cerebellum

• Automatic processing centre

• Constantly receives memory input from muscles

• Compares intended movement programmed by cerebral cortex with actual events

• Co-ordinates + smooth complex sequences of skeletal muscle contractions

• Essential for all skilled motor activities (eg. baseball)

• Injury to the cerebellum can result in Ataxia

Cerebellum Receives memory input from

• Muscles

• Joints

• Tendons

• Equilibrium

• Visual Receptors

Ataxia

• Degenerative CNS disease

• Progressive

• Problems with motor function

• Symptoms can mimic alcohol intoxication

Motor Pathways

• Pyramidal Tracts

• Corticospinal Tracts

• Extrapyramidal Tracts

• Upper Motor Neurons

• Lower Motor Neurons

The Corticospinal Tract

• Neurons from the motor cortex to the spinal cord that control voluntary movement, where they synapse directly onto somatic motor neurons

• Pathway is sometimes called the pyramidal tract

The Pryamids

The part of the Corticospinal tract that crosses the midline in the medulla

Pyramidal Tract

• Composed of a single neuron which extends from the pre-central gyrus to the ventral horn of the spinal cord

• Excitation in action

Pyramidal Tracts Function

• Direct pathway responsible for voluntary, skilled, and precise movements; particularly of Limbs

Pryamidal Tracts Location

• 90% decussate in medulla then descend as the the lateral corticospinal tracts

• Crossover means that each side of the brain controls the opposite side of the body

• 10% decsend uncrossed as anterior corticospinal tracts then cross in spinal cord

Nuclei in grey matter of the Medulla Functions

• Controls involuntary functions

• BP, Breathing, Swallowing, and Vomiting

Extra Pyramidal Tracts

• Upper Motor Neurons

• Lower Motor Neurons

Extra-Pyramidal Tracts

• Originates in brainstem

• Modulates Motor activity

• Neurons from basal ganglia also influence body movement

• Multiple synapses in the CNS

Extra-Pyramidal Tract Actions

• Indirect pathways from pre-central gyrus to lower motor neurons

• Inhibitory and excitatory in action

• Control unconsciousness movements

• The pyramidal and extra-pyramidal tracts interact

Upper Motor Neurons

• Neurons extend from primary motor cortex to the ventral horn of the spinal cord

• These are CNS neurons with cell bodies in brain

Upper motor Neurons Locations

• Neurons from basal ganglia also influence body movement

• These neurons have multiple synapses in the CNS

• Form the extra-pyramidal tract

Upper motor neurons Spinal Cord

• Upper motor neurons carry impulses from the primary motor area of the cerebral cortex + Synapse with inter neurons and lower motor neurons

• Axons from one cerebral hemisphere cross over and synapse with motor neurons on the opposite side of the spinal cord

Upper motor Neuron 2 spinal cord tracts

• 2 spinal cord tracts conduct impulses along axons of upper motor neurons

• Anterior + Lateral contricospinal tracts

• Synapse with lower motor neurons or inter neurons in the ventral horns

Lower Motor Neurons

• All somatic motor pathways controlling movement, converge on lower motor neurons (LMN)

• Input to lower motor neurons come from:

• Local interneurons, upper motor neurons , basal nuclei neurons and cerebellar neurons

Lower Motor Neurons Axons

• Axons of LMN’s extend out of the brain stem and stimulate skeletal muscles in the head, limbs + trunk

• Peripheral neurons

• Cell bodies Located in ventral horn of the spinal cord

Lower Motor neuron Pathways

• There are several pathways from the brain to the ventral horn

• The LMN is the only pathway from the ventral horn to the effector

Upper Motor Neuron Damage Causes

• Multiple sclerosis

• Stroke

• Brain or spinal cord injuries

Upper Motor Neuron Damage Symptoms

• Muscle stiffness, weakness; poor motor control

• Exaggerated reflexes

• Spastic paryalysis

• Removal of inhibitory influences of upper + lower motor neurons; opposite side of body

Spastic Paralysis

• Reflexes exaggerated

• Muscle tone increased

• Pathological reflexes appear

Lower Motor neuron damage causes

• Viruses/infections

• Peripheral nerve trauma

Lower Motor Neuron Damage Symptoms

• Muscle paralysis or weakness

• Loss of relfexes

• Muscle atrophy

• Flaccid paralysis

• Damage to muscles on the same side of body produces a lack of voluntary control and reflexes and muscle remains flaccid

Organization of the Autonomic Nervous System (ANS)

• ANS is part of the peripheral nervous system (PNS)

• 1. Somatic Nervous system

• 2. Autonomic Nervous System

Somatic Nervous System

Controls responses at skeletal muscles

Autonomic Nervous System

• Controls smooth and cardiac muscles and many glands

• Sub-divided into sympathetic and parasympathetic nervous systems

Sympathetic

• Predominates under stressful conditions

• Regulated by hypthalamus

• (+) HR

• blood vessels dialate

• Liver produces more glucose

• Digestion is low priority

Parasympathetic

• Predominates under resting conditions

Divisions of the ANS

1. Sympathetic Nervous System

2. Parasympathetic Nervous System

Sympathetic Nervous System

• Fight or Flight response

• Daily life (controls blood flow)

Parasympathetic Nervous System

• Para - means beside or along side

• Controls quiet activities of daily life eg. digestion

• Mostly antagonistic in control of a single target tissue; sometimes work cooperatively

ANS maintains Homeostasis

• Primary function is to maintain homeostasis

• Coordinates:

• Cardiovascular function

• Respiration

• Digestion

• Excretion

• Reproduction

• ANS works closely with the endocrine system to maintain homeostasis

Integration of autonomic function

• Sensory info from somatosensory + visceral receptors go to homeostatic control centres in the brainstem + hypothalamus

• These centres monitor + regulate important functions

Autonomic control centres

• Monitor + regulate important functions

• BP

• Temp control

• Respiration

• water balance

• Motor output from Hypothalmus + brainstem creates responses in the autonomic + endocrine systems

Hypothalamus Control

• Temp

• HR

• Hunger

• Thirst

• Fluid concentration

Medulla Controls

• Reflex control centres

• More complex reflexes

Spinal Cord Controls

• Reflex control centres in sacral spinal cord

• Simple reflex centres

• Autonomic influences activities of cardiac, vasomotor, respiratory and digestive centres

Antagonistic Control is Hallmark of the ANS

• Antagonistic Control: one branch is excitatory another inhibitory

• 2 systems sometimes work together

• In some pathways the neurotransmitter receptor determines the response of target tissue

Autonomic Pathways have 2 efferent Neurons in series

• Pre-ganglionic neuron

Pre ganglionic Neuron

Originates in CNS and projects to an Autonomic in the PNS before synapsing with a post-ganglionic neuron