Central Nervous System

**Central nervous system**

* **integration and command center**
* **Brain**
* **Spinal cord**

Gray matter

* non-myelinated material (cell bodies, dendrites, telodendrites)
* Nuclei – in the CNS
* Ganglia – in the PNS

White matter

* myelinated axons
* Tracts – axons in the CNS
* Nerves – axons in the PNS

**Tracts**

axons running to or from

Types Of Tracts

**Projection**

**Association (arcuate)**

**Commissural**

**Projection**

vertical tracts, responsible for the communication between the cerebral cortex and lower CNS

**Association (arcuate)**

* **connect gyri within the same cerebral hemisphere**

**Commissural**

* **connects gyri between left and right hemispheres**

Protection of CNS

**Bones of the skull and vertebral column**

Meninges

Cerebrospinal fluid

Blood Brain Barrier

**Meninges**

three CT membranes surrounding the brain

**Dura Mater**

**Arachnoid Mater**

**Pia Mater**

**Dura Mater**

**superficial layer, consists of two layers of fibrous CT**

**Arachnoid Mater**

loose middle layer

**Pia Mater**

deepest, attaches tightly to the brain following every convolution.

Cerebrospinal fluid

found in the ventricles

subarachnoid space around the brain

spinal cord

Function of Cerebrospinal fluid

* Gives buoyancy to the brain and spinal cord – keeps it from being damaged by its own weight
* Cushions and protects
* Transports materials

**Blood Brain Barrier**

capillaries are less permeable due to tight junctions between endothelial cells and astrocytes

Function of **Blood Brain Barrier**

* Helps maintain a constant environment for the brain


* Very selective- fat soluble materials, glucose, and select ions and amino acids are allowed to pass, others are not

Metabolic Requirements of the CNS

Neurons rely on a constant supply of oxygen and glucose to produce ATP for active transport of ions and neurotransmitters

* Oxygen diffuses across the BBB
* Under normal circumstances glucose is the only energy source for neurons

Where and how is glucose transported?

Glucose is transported from the plasma into the interstitial fluid by insulin independent membrane transporters

What does Hypoglycemia lead too?

* leads to confusion, unconsciousness and death

Regions Of CNS

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**Cerebrum**

**Diencephalon**

**Brainstem**

**Cerebellum**

**Spinal cord**

**Cerebrum**

integration of sensory/motor, higher functions

**Diencephalon**

* **initiate drives and emotions**

What organs are under **Diencephalon**

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* **Epithalamus**
* **Pineal gland**
* **Thalamus**
* **Hypothalamus**
* **Pituitary gland**

**Brainstem**

* **basic functions to maintain life**
* **Midbrain**
* **Pons**
* **Medulla oblongata**

**Cerebellum**

coordination

**Spinal cord**

reflexes

Plasticity of the Brain

architecture of the cortex is determined by genetic and developmental processes __but it can be modified__ due to “use-dependent competition”

can be remodeled throughout life or limited time

Functional Areas of the Cerebral Cortex

**Sensory areas**

**Motor areas**

**Association areas**

**Sensory areas**

* **process afferent impulses, interpret sensations**

**Motor areas**

* **planning and initiating muscular movement**

**Association areas**

* **combining information from multiple areas and processing them together, involved in higher functions**
* **Ex: Language, judgment**

Cerebral Cortex: Sensory Areas

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**postcentral gyrus in the parietal lobe**

**Somatosensory association**

**Primary auditory**

**Auditory association area**

**Olfactory cortex**

**Gustatory cortex**

**Primary visual cortex**

receives sensory input from the retina to the occipital lobe. Data only.

**Visual association area**

interprets the raw data and puts it into context. Surrounds the primary.

**Primary auditory**

receives sensory input from the vestibulocochlear nerve to temporal lobe.

**Auditory association area**

**lies posterior to primary, interprets sound into context**

**Olfactory cortex**

found on medial aspect of temporal lobe. Sensory input from olfactory nerves.

Linked limbic system – tied to emotions and memories

**Gustatory cortex**

* **perception of taste, found in the insula**

Cerebral Cortex: Motor Areas

**Primary motor cortex**

**Premotor cortex (association)**

**Primary motor cortex**

controls somatic motor neuron output

Precentral gyrus of the frontal lobe

Control is contralateral

How is output controlled by

higher motor areas and input from the cerebellum

Cortical Homunculus

Amount of cortex devoted to each area relates to which regions have the most precise control.

**Premotor cortex (association)**

* **anterior to the primary motor cortex in the frontal lobe**
* **Responsible for coordinating learned motor skills**
* **Examples: typing, driving, playing the piano**

**Basal Nuclei**

gray matter

Adjust the stop, start and intensity of movements after receiving input from cerebral cortex and substantia nigra

What does the Lesions of nuclei lead too

increase motor output leading to increased muscle tone, difficulty initiating movement, and involuntary muscle movement

Cerebral Cortex: Association Areas

**Prefrontal cortex**

**Prefrontal cortex**

* **involved with intellect, recall, reasoning, judgment, concern for others, personality traits, and management of emotions**
* **Develops later in life and is impacted by social environment**

Cerebral Cortex: Language Areas

**Language areas**

**Language areas**

* **surrounds lateral sulcus, usually in the left hemisphere only (in 95% of population)**
* **Receives input from auditory and visual senses**
* **Coordinates with the motor cortex to carry out motor skills involved in speech and writing**

__**Wernicke’s area**__

* **Language comprehension and formulation of coherent patterns of speech**
* **If damaged, you can still speak but it won’t make sense in context**

__**Broca’s area**__

* **speech production and word formation, associated with motor cortex**
* **If damaged, you know what to say but struggle in forming the words**

Limbic System

emotional brain

consists of tracts and nuclei of the medial cerebrum, anterior thalamus, and hypothalamus

Function of Limbic System

* emotional and behavioral
* Linked to prefrontal cortex, sometimes logic overrides emotion or vice versa
* Long term memory storage and retrieval

Limbic system structures

**Amygdala**

**Cingulate gyrus**

**Hippocampus**

**Amygdala**

* **recognizes angry or fearful expressions and assesses danger** 

**Cingulate gyrus**

* **role in expressing emotion and resolving mental conflicts**

**Hippocampus**

role in memory along with amygdala

How Emotions Influence Physiological Functions

Emotions can influence your autonomic nervous system because they are both controlled by the hypothalamus

Memory

Memory is the storage and retrieval of information

The three principles of memory are

* Storage – occurs in stages and is continually changing (stored in regions that need them)
* Processing – accomplished by the hippocampus and surrounding structures 
* Memory traces – chemical or structural changes that encode memory (pathways)

The two stages of memory

* Short-term memory (working memory) 
* STM lasts seconds to hours and is limited to 7-12 pieces of information
* Only 5% of sensory input is transferred to STM

Long-term memory (LTM) has    limitless capacity

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

Emotional state

Rehearsal

Association

Automatic memory

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

The two categories of memory are

Fact (declarative) memory

Skill (procedural) memory

Fact (declarative) memory

* Entails learning explicit information (names, dates)
* Is related to our conscious thoughts and our language ability
* Is stored with the context in which it was learned

Skill (procedural) memory

* less conscious than fact memory and involves motor activity  (ex: riding a bike)
* It is acquired through practice or repetition
* Skill memories do not retain the context in which they were learned
* Hard to unlearn
* Stored in the premotor cortex

How Memories are Formed

Long-term potentiation

Long-term potentiation

* prolonged increase in synaptic strength 
* Repetitive stimulation results in modification of synapses that increase the ability of pre-synaptic neurons to stimulate post-synaptic neurons
* Necessary for memory trace formation

Types of synaptic modifications that can occur as a result of LTPs

* Number and size of presynaptic terminals may increase
* More neurotransmitter is released by presynaptic neurons 
* Dendritic spines change shape
* Extracellular proteins are deposited at synapses

**Hypothalamus**

* **slightly anterior and inferior to the thalamus**
* **Important in maintaining body homeostasis and behavioral drives**

Autonomic control center

(Hypothalamus)

* Controls release of catecholamine from the adrenal medulla
* Controls ANS centers in the brain stem and spinal cord, BP, HR, digestive tract, respiration rate, pupil size

Emotions

heart of limbic system, basic primitive drives such as fear, anger, pleasure

Regulates body temperature

thermostat, initiates cooling or heating mechanisms

Sleep-wake cycles

acts with pineal gland to set cycles in response to light and dark

Food intake

responds to changes in levels of nutrients and hormones. Contains satiety and feeding centers

Water balance and thirst

osmoreceptors that detect concentrations of body fluids, triggers anti-diuretic hormone (ADH)  and thirst centers

Hormones

* Produces releasing or inhibiting factors which controls the release of hormones from the anterior pituitary
* Produces posterior pituitary hormones, ADH and oxytocin

**Midbrain**

superior portion of the brain stem

* **Corpora quadrigemina – four protrusions on the dorsal surface, contain sensory nuclei**
* **Superior colliculi – visual reflexes**
* **Inferior colliculi – auditory reflexes**

**Substantia nigra**

* **axons linked to cerebral basal nuclei, release dopamine, controls motor output**
* **Degeneration of these neurons causes Parkinson’s disease**

**Pons**

bulging region between midbrain and medulla, anterior to cerebellum

Pontine nuclei

(**Pons)**

relay station for tracts between motor cortex and cerebellum

**Pneumotaxic and apneustic respiratory center**

(Pons)

**works with medulla to maintain rhythmic breathing**

**Medulla Oblongata**

base of brain stem, blends inferiorly with the spinal cord

**Pyramids**

* **longitudinal ridges on the ventral surface**
* **Contains motor tracts that cross over (decussation) before they continue down the spinal cord**

**Cardiovascular center**

(Medulla Oblongata)

**adjusts force and rate of heart contraction and blood pressure**

**Respiratory center**

(Medulla Oblongata)

* **controls rate and depth of breathing, works with pons for rhythm**
* Vomiting, swallowing, coughing, sneezing, hiccups

**Reticular Formation**

* **loose cluster of neurons extending through the brain stem to the thalamus, hypothalamus, cerebellum and spinal cord**
* **Responsible for the arousal (alertness) of the brain**

**Reticular Activation System (RAS)**

neurons sending constant impulses to the cortex via the thalamus to keep the cortex conscious and alert

Damage suffered by a jolt to the brain stem may result in permanent unconsciousness

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
* A typical sleep pattern alternates between REM and NREM sleep

Stages of NREM

* Stage 1
* Dosing off, jerking or feel of falling can happen


* Stage 2/ Stage 3
* Difficult to arouse


* Stage 4
* Deep sleep

Characteristics of NREM sleep

* Low frequency waves across cerebral cortex
* Unconscious adjustments of body position
* Sleep walking occurs in NREM

Characteristics of REM sleep 

* Vital signs increase (BP, RR, HR)
* Neuronal activity is high (pons, limbic system)
* Skeletal muscles (except ocular muscles) are inhibited
* Most dreaming takes place, reduced activity of prefrontal cortex

What regulates the sleep cycle?

suprachiasmatic and preoptic nuclei of the hypothalamus

What appears to be a sleep inducing chemical?

Adenosine

* Slows down neural activity by binding to receptors on neurons
* Caffeine blocks adenosine receptors

But adenosine keeps building which is why we crash after a caffeine high

Importance of Sleep

* NREM sleep is the restorative stage
* REM sleep may be a reverse learning process where uneccessary information is purged from the brain (one hypothesis)
* Those deprived of REM sleep become moody and depressed
* Daily sleep requirements decline with age

Sleep Disorders

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Narcolepsy

Insomnia

Sleep apnea

Sexomnia

Night Terrors

Sleepwalking