NUR 305 Neurological System I

The Nervous system consists of

Central Nervous System (CNS)

1. Brain

   • Receives and processes sensory information, initiates responses, stores memories, generates thoughts and emotions.

2. Spinal Cord

   • Conducts signals to and from the brain, controls reflex activities.

Peripheral Nervous System (PNS)

1. Motor Neurons

   • CNS to muscles and glands

     →

     1. Somatic Nervous System

     • Controls Voluntary Movements

     2. Autonomic Nervous System

     • Controls Involuntary Movements

       →

       1. Sympathetic Division

          • Fight/Flight

       2. Parasympathetic Division

          • Rest/Digest

2. Sensory Neurons

   • Sensory organs to CNS

What 3 things is the Nervous System responsible for?

1. Movement

2. Sensation

3. Cognition

What does the Central Nervous System consist of?

Brain and Spinal Cord

What does the Peripheral Nervous System consist of?

Motor Neurons and Sensory Neurons

Where does the Somatic Nervous System stem from?

Motor Neurons

Where does the Autonomic Nervous System stem from? What divisions exist under the Autonomic Nervous System?

1. Motor Neurons

2. Sympathetic and Parasympathetic

What are the functions of Neurons?

1. Generate action potentials.

   • Through Na+/K+ pumps

   • Action potentials are specific/exclusive to neurons.

2. Transmitter cells.

3. Carry messages to and from the brain and spinal cord.

What are the functions of Glial Cells?

Description

• Support and protect neurons.

• Do not generate action potentials (exclusive to neurons) but have a resting membrane potential.

• Produce CSF.

  • Contains proteins, glucose, and electrolytes

What are the functions of Glial Cells in the CNS?

1. Astrocytes → Recycle glutamate into vesicles.

2. Microglia → Immune system of brain (most active at night)

3. Oligodendroglia → Produce myelin in the CNS

4. Ependymal Cells → Located on roof of lateral ventricles (spaces) in brain (There are 4 ventricles in the brain) → Generate CSF

What are the functions of Glial Cells in the PNS?

1. Schwann Cells → Produce myelin in the PNS

2. Satellite Cells → Supportive function

Electrical Impulses

• Info passed between neurons by chemicals.

• Can be excitatory (most) or inhibitory.

  • Action potentials are sent or inhibited.

• Along the axons, the information passes electrically.

Neurons can synapse with:

1. Neurons

2. Muscles

3. Glands

Synaptic Transmission

A small burst of neurotransmitters is released.

The neurotransmitters stimulate or inhibit action potentials.

Neurotransmitters are chemical messengers that are either ____ by enzymes or _____. They are also usually _____ for the next transmission.

destroyed; reabsorbed; recycled

In the neuromuscular junction (the area where nerves synapse with muscles) the neurotransmitter is _____?

Acetylcholine

Dopamine

Description

• Promotes smooth, coordinate muscle movement.

Deficiency

• Involved in Parkinson’s Disease.

Excess

• Involved in Schizophrenia.

Norepinephrine & Epinephrine

Description

• Stimulates adrenergic receptors in sympathetic nervous system (causes vasoconstriction)

• Keeps vasomotor tone → keeps BP stable

• Adrenergic receptors located in medial muscle layer of arteries.

Receptors

• Alpha 1 & 2

• Beta 1 (HR, rhythm)

• Beta 2 (Inc pumping/contraction of heart) / (Bronchodilation)

• Beta 3

Serotonin

Mood regulation, inhibits pain.

Acetylcholine

Description

• Stimulates cholinergic receptors in parasympathetic nervous system & neuromuscular junction.

Deficiency

• Due to damaged receptors

• Involved in Myasthenia Gravis.

GABA/Glutamate

• Excitatory

• Involved in addiction

• Involved in award system

• Recycled by astrocytes

Endorphins/Enkephalins

Endogenous opioid system.

• “Runner's high” feeling

Substance P

Pain transmission

Melatonin

Sleep regulation

Myelin

Lipoprotein that increases speed of conduction.

• Especially on nerves w/ large axons

• Some small nerves are myelinated too.

• Present in CNS

"Unmyelinated" Axons

Smaller nerves, slower transmission.

• Visceral pain

• Ex) GI pain.

What are characteristics of Neurons?

1. Do not have the ability to divide.

2. Losses due to aging or injury cannot be replaced.

   • Once the NS matures, by age 2, that’s it.

3. Not all cell death results in loss of functioning.

   • Other areas will pick up the functions is one area is damaged w/ time.

4. Undamaged neurons in the brain will assume functions of damaged neurons (“plasticity”).

   • Neuroplasticity easier in childhood.

5. Require a constant oxygen and glucose supply.

   • >5-6 mins w/o O2 leads to death.

6. Neurons are vulnerable to hypoxia and hypoglycemia.

   • See Point 5 above

What are injuries to the NS that can be fixed?

Severed Peripheral Nerves

• Can regenerate to a point to reestablish connections.

What are injuries to the NS that cannot be fixed?

Severed Brain and Spinal Cord Axons

• Result in paralysis

• Loss of sensation below the area of damage.

How long the brain can go without oxygen?

5-6 minutes MAX

What does the cerebrum contain?

• Frontal lobe

• Parietal lobe

• Occipital lobe

• Temporal lobe

Cerebrum Function

Cognition & Abstract thinking.

What does the Diencephalon contain?

• Thalamus

• Hypothalamus

Cerebellum Function

Balance and coordination.

Thalamus Function

• Relay station for motor and sensory signals to the cerebral cortex.

  • Carries/coordinates different areas of the brain.

• Plays a role in motor activity, emotion, memory, arousal, and other sensorimotor association functions.

• Regulates consciousness, sleep, and alertness.

Brain Stem Function

Autonomic function

What does the Brain Stem contain?

• Midbrain

• Pons

• Medulla Oblongata

Hypothalamus Function

• Releases precursor/tropic hormones

• Thermoregulation

Most individuals with damage to the left hemisphere develop Aphasia. What is Aphasia?

A disorder that makes it difficult to speak or understand language.

What is the difference between Expressive and Receptive Aphasia?

Expressive Aphasia

• Person knows what they want to say, but what they say doesn’t make sense.

Receptive Aphasia

• Person cannot understand what is being said to them, but can speak normally.

If you hit the back of your head on the occipital region, which sense would you expect to lose?

Vision

Ipsilateral vs. Contralateral Nerves

Ipsilateral

• Nerve fibers that run on the same side of the body they originate on.

• Ex. Nerve fiber starts on right hemisphere, is expressed on right side of body.

• Ex. Optic nerves

• (20%) of corticospinal and spinothalamic nerve fibers.

Contralateral

• Nerve fibers that run on the opposite side of the body they originate on.

• Ex. Nerve fiber starts on left hemisphere, is expressed on right side of body.

• The majority of corticospinal and spinothalamic nerve fibers (80%)

Cervical Nerves

8 pairs

Thoracic Nerves

12 pairs

Lumbar Nerves

5 pairs

The Brain Regions

If you have a stroke on the right hemisphere, in most people the deficits will be on the left. Why is this true?

Most nerves are contralateral.

The Meninges

1. Layers of membranes that envelop and protect the CNS.

2. There are 3 meningeal membrane layers.

   • Dura mater arachnoid mater, pia mater.

3. Between each meningeal membrane layer there is a potential space.

   • Skull (Epidural Space) Dura Mater (Subdural Space) Arachnoid Mater (Subarachnoid Space) Pia Mater

4. The middle meningeal artery runs very close to the skull bone above the dura mater.

   • Middle meningeal artery commonly ruptures and causes an epidural hematoma.

     • First sign is loss of consciousness.

What leads to a Subdural Hematoma?

• There is a network of veins within the subdural space.

• Head trauma often causes rupture of subdural veins, which causes a subdural hematoma.

T/F: CSF is contained beneath the arachnoid membrane within the subarachnoid space.

True

3 Meninges

1. Dura Mater: outer layer, lines skull

2. Arachnoid Mater: middle layer, contains blood vessels

3. Pia Mater: inner layer, covers brain

3 Potential Meningeal Spaces

Epidural: outside dura.

Subdural: between dura and arachnoid.

Subarachnoid: deep to arachnoid, filled with CSF.

• Loss of CSF from nose/ears may indicate subarachnoid bleed.

Cerebrospinal Fluid (CSF)

• Made in choroid plexuses (roofs of ventricles).

  • Filtration of plasma from capillaries through ependymal cells

  • Takes electrolytes, glucose from plasma.

• Cushions and nourishes brain.

• Useful for diagnosing meningitis (cloudy CSF), bleeds, MS (multiple sclerosis).

• Excessive accumulation of CSF → Hydrocephalus

The Flow of Cerebrospinal Fluid

Created/Filtered in: 4 Ventricles

Flow

Lateral Ventricle → Third Ventricle → Fourth Ventricle → Subarachnoid Space

Mean Arterial Pressure

MAP = diastolic pressure + 1/3 (systolic BP-diastolic BP)

Intracranial Pressure (ICP)

Normal Range

• 0-15 cmH20 or mmHg

Cerebral Perfusion Pressure (CPP)

Description

• Pressure it takes to completely perfuse the brain.

• Bleeds can happen if CCP is high.

Calculation

• CCP = MAP - ICP

Optimal Range

• 70-90 mmHg

A high ICP = A ___ CPP

low

Blood Supply to the Brain

• Supplied by the internal carotid (2, anterior) and vertebral (2, posterior) arteries.

• Arterial circle (Circle of Willis) helps ensure flow.

  • New veins can form w/ time from here if damage were to occur.

• Blood flows through the brain at a rate of: 800 to 1000 mL per minute.

• CO2 level affects CNS blood flow.

  • Increases in CO2 will increase cerebral blood flow & arterial blood pressure.

  • Causes vasodilation (leaky blood vessels)

  • Can worsen cerebral edema.

Anterior Cerebral Artery

Supplies frontal lobes.

Middle Cerebral Artery*

Supplies the Frontal lobe.

Supplies the lateral surface of the temporal and parietal lobes.

• Includes motor, sensory, speech centers.

• Most frequently occluded artery In a stroke.

Lenticulostriate Arteries

Small, deep penetrating arteries that branch from the middle cerebral artery.

Posterior Cerebral Artery

Supplies the temporal & occipital lobes of cerebral hemispheres.

• If lack of blood flow, can affect vision.

Circle of Willis

The middle cerebral artery supplies a large area of brain tissue.

• When occluded, it causes deficit of a major region of the brain.

• Most strokes involve a branch of the middle cerebral artery.

Autoregulation of Cerebral Blood Flow

The arteries that comprise the circle of Willis in the brain normally maintain a constant flow of blood within the brain.

• Baroreceptors help regulate pressure in the brain.

• Optimizes blood flow when BP is low — peripheral vessels constrict, cerebral vessels dilate.

When does Autoregulation of Cerebral Blood Flow not work?

When BP is either too high or too low.

• Autoregulation is overridden

• Ex) 50/40 mmHg

• Ex) 240/120 mmHg

Cranial Nerves

12 of cranial nerves branch directly from the base of the brain.

• Some only carry sensory fibers.

• Some only carry motor fibers.

• Some carry both.

• Each nerve travels from the brain through the foramen ovale to its destination.

T/F: All of the cranial nerves mostly supply the head and neck.

False; Most of the cranial nerves mostly supply the head and neck. The Vagus nerve (CN X) is the exception. The vagus nerve has nerve fibers in the heart, respiratory (accessory) muscles, stomach, and gallbladder.

T/F: Cranial nerves can act as antennae that can sense changes in intracranial pressure.

True

CN I

Olfactory Nerve | Sensory

CN II

Optic Nerve | Sensory

CN III

Oculomotor Nerve | Motor

CN IV

Trochlear Nerve | Motor

CN V

Trigeminal Nerve | Both

CN VI

Abducens Nerve | Motor

CN VII

Facial Nerve | Both

CN VIII

Acoustic Nerve | Sensory

CN IX

Glossopharyngeal Nerve | Both

CN X

Vagus Nerve | Both

CN XI

Spinal Accessory Nerve | Motor

CN XII

Hypoglossal Nerve | Motor

Application of the Glasgow Coma Scale (GCS)

• Used in patients that are unconscious or have altered levels of consciousness / mental status.

• Assesses:

  1. Motor response

  2. Eye opening

  3. Verbal response.

• Assess this, vital signs, and pupil response.

Level of Impairment of GCS*

• Mild: 13-15

• Moderate: 9-12

• Severe: 3-8

What does the Spinal Cord consist of?

1. White matter

2. Gray matter

3. Ascending Fibers/Afferent Tracts

4. Descending Fibers/Efferent Tracts

White Matter (Spinal Cord)

Comprised of nerve fiber tracts/pathways.

Gray Matter (Spinal Cord)

Neurons

• Interneurons connect the CNS to the PNS

Ascending Fibers/Afferent Tracts (Spinal Cord)

Carry sensory information from body back to the brain.

• Afferent/Ascending → Body UP to Brain

Descending Fibers/Efferent Tracts (Spinal Cord)

Carry motor impulses from the brain to the PNS.

• Descending/Efferent → Brain DOWN to body.

What are the detailed components of the Peripheral Nervous System?

Nerves

• Bundles of nerve fibers.

• Each fiber is part of the neuron.

• Work like an “information” highway

31 Spinal Nerve Pairs

• 8 cervical

• 12 thoracic

• 5 lumbar

• 5 sacral

• 1 coccygeal

Ganglia

• Collections of nerve cell bodies outside the CNS.

Spinal Nerves

• Arise from dorsal and ventral surfaces of the spinal cord.

• Each spinal nerve is comprised of a dorsal root + a ventral root.

  • Each “root” formed from 6–8 rootlets.

Somatic (Voluntary) PNS

• 31 pairs of spinal nerves

• 12 pairs of cranial nerves

Automatic (Involuntary) PNS

Controls the Following

• Smooth muscles

  • Arteries, GI tract, lungs

  • Adrenergic receptors

• Cardiac muscle

• Glands

Spinal Cord Nerves Mneumonic

Breakfast at 8

• Cervical (8)

Lunch at 12

• Thoracic (12)

Dinner at 5

• Lumbar (5) + Sacral (5)

Dancing till 1

• Coccygeal (1)

Levels of Injury and Extent of Paralysis

Injury at C 3-5 or Higher

• Requires assistance mechanical ventilation to support breathing.

• Loss of GI, walking, arm movement, breathing.

• Quadriplegia

Injury at C6

• Quadriplegia

• Loss of GI function and walking

Injury at T6

• Paraplegia

• Loss of GI function and walking

• May have shoulder movement

Injury at L1

• Affects walking and bowel/bladder if complete injury

• Paraplegia

Injury at T6 or Higher - What should we be concerned about?

Breathing

Afferent Nerves are _____ nerves.

sensory

Input = _____. To the brain = ____.

sensory; afferent

Efferent Nerves are _____ nerves.

motor

Output = _____. From the brain = ____.

motor; efferent

Interneurons connect the ____ and ____ neurons in the spinal cord.

sensory; motor

Dermatome

Area of the skin innervated by a given pair of spinal sensory nerves.

The Autonomic Nervous System (ANS)

Responsible for maintaining the internal environment of the body (homeostasis).

• Regulates Cardio, Gastro, and Glands

Controls smooth muscles.

Controls unconscious responses such as:

• Heart rate

• Blood pressure

• Intestinal motility