Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
9/11/2011
1
Neural Communication
Overview of CNS / PNSElectrical SignalingChemical Signaling
Central Nervous SystemPeripheral Nervous System
• Somatic = sensory & motor
• Autonomic = arousal state– Parasympathetic= relaxation, not aroused
– Sympathetic = fight or flight response, stress
Communication in the Nervous System
• Electrical Signals– Discrete on/off signal – Fast over long distances– Caused by movement of positive (Na+, K+) or negative (Cl‐) salt ions in or out of the neuron
– 2 types: synaptic potentials (input signal) and action potentials (transmission signal)
• Chemical Signalsbetween neurons:– Slower but only used for short distance (synapse)
– Chemicals provide selectivity that electricity does not have due to lock and key binding with spe
as hormones:– Sustained effects throughout body
4 Common Components of a Neuron
• Dendrites – input, receives neurotransmitters
• Soma – processing, decision• Axon – transmits signal• Terminal Buttons – output, release neurotransmitters to target
• Myelin Sheath – insulates axon• Synapse ‐ junction between neuron and target
9/11/2011
2
TRANSMISSION and NT RELEASE
INPUT and PROCESSINGTransmitter-gated receptor channels
EPSP / IPSP produced by ion entry & exit
Temporal & Spatial summation occurs in the soma
Overview of Electrical Signaling Input – Dendrites
Synaptic Potentials• Neurotransmitters open the ion channels to provide input
• Movement of positive or negative ions creates the electrical synaptic potential
Input – DendritesSynaptic Potentials
• Depolarization = Na+ enters increasing resting potential towards zero (less polarized)
• Hyperpolarization = K + exits decreases resting potential• Missing from figureare the pumps thatmove Na+ outsideand K + inside usingenergy
Processing / Decision‐making – SomaSummation of Synaptic Potentials
• Depolarization & hyperpolarization travel from dendrites to soma where charges summate at start of axon
• If sum equals threshold (‐50mV) then action potential• If sum is less than threshold then nothing
9/11/2011
3
Soma: Temporal & Spatial Summation• Additional inputs that occur before the pumps return ions can add together
Can occur through multiple inputs or a single neuron
Temporal Spatial
• Increased summation = the closer in space & time.
INPUT and PROCESSING
Transmitter-gated receptor channels
EPSP / IPSP
Summation
TRANSMISSION and NT RELEASE
Voltage-gated channels
Action Potentials = all or nothing principle
Synaptic events to release neurotransmitters exocytosis
10
1. Threshold opens voltage‐gated Na+ channels = Rising Phase: Na+ Entry2. After Na+ entry, voltage‐gated K + channelsopen = Falling Phase: K+ Exit3. The Na+/K+ pump restores ion concentrations so next signal can be sent = Refractory Period: no action potentials
0 1 2 3 4 msec
+30 mV
-70 mV
Visualizing ionic transport during the action
potential.
+30 -70-50
+30 -50+30 ↓
-75 +30 ↓ +30
Pumps working
9/11/2011
4
Output – Terminal ButtonsReleasing Neurotransmitter
• Neurotransmitters stored in vesicles at terminal button
• Action potential at terminal releases neurotransmitter
• Neurotransmitter binds toreceptors on target –produces synaptic potentials
• Neurotransmitters separate from receptors
• Neurotransmitters recycled or eliminated from the synapse
Chemical Signaling:Neurotransmitters and Receptors
• Neurotransmitters have a specific shape and bind with matching sites (lock & key)
• Allows 2 neurotransmittersto act in different ways onthe same target
• Eliminates interference orcross‐talk between closesynapses
Common Neurotransmitters• Acetylcholine (ACh): parasympathetic nervous
system (induces calm, resting state) - muscles• Serotonin (5-HT): sleep & mood• Dopamine (DA): pleasure center & movement• Norepinephrine (NE): sympathetic nervous system
(induces aroused, heightened state)• Glutamate: general excitatory neurotransmitter• GABA: general inhibitory (opens Cl- channels)• Peptides: regulatory actions to modulate systems
Common Drug Actions
• Agonist increases the effect of a neurotransmitter• Antagonist decreases the effect of a neurotransmitter• Ways drugs can be Agonists:
– Mimic the NT & artificially activate the receptors– Increase the production of NT– Inhibit metabolism or enzymatic breakdown of NT– Inhibit or block NT reuptake from synapse– Increase the release or amount of NT in vesicles
• Ways drugs can be Antagonists– Block access to the receptor– Inhibit production of the NT– Breakdown or inactive NT (speed metabolism)– Cause NT leakage from vesicles
9/11/2011
5
Neuroanatomy Slides
Hindbrain, Midbrain, ForebrainCortex LobesSystems
Brain Divisions: Hindbrain
Spinal Cord
Pons
MedullaCerebellum
Hindbrain• Hindbrain includes the pons, medulla, and cerebellum.
• Pons & medulla contain nuclei (areas) devoted to life sustaining functions such as respiration, cardiac function, and general consciousness). Damage to this area is serious usually resulting in coma or death.
• The cerebellum was originally thought to be mostly involved with coordinating sensory / motor signals to produce coordinated movements but now we realize that it has many more complex functions including an important role in learning.
Brain Divisions: Midbrain
SuperiorColliculus
Tectum
1
1
InferiorColliculus
9/11/2011
6
Midbrain• Midbrain includes the tectum, inferior colliculus, and superior colliculus
• The tectum is a higher order of regulatory functioning containing the nucleus for pain management (periaquaductal gray) and nuclei that distribute serotonin (raphe), norepinephrine (locus coeruleus), and dopamine (substantia nigra)
• The colliculi are used for localizing and orientating to auditory stimuli (inferior colliculus) and visual stimuli (superior colliculus).
Brain Divisions: Forebrain
CorpusCallosum
Thalamus
Hypothalamus
Pituitary Gland
Basal Ganglion
Forebrain• Forebrain includes subcortical structures with specific functions that are duplicated in both
hemispheres and cortex which has functions that are more lateralized or specific in nature and not duplicated on both sides of the hemispheres.
• The corpus callosum is a large bundle of axons that connect the two hemispheres allowing the cortex of the brain to function as a single unit.
• Subcortical structures:– Thalamus – more than a sensory relay station, this is where our brain uses attention to filter important and
unimportant incoming sensory stimuli (for example, habituation to the heat/air conditioning fan in the room so you no longer perceive it until your attention is called to the stimulus is happening in the thalamus)
– Hypothalamus – located under the thalamus, this structure is a collection of nuclei that maintain our internal body states and homeostasis including sleep / wake cycle, hunger, thirst, body temperature, and hormonal control of growth, sex and reproduction, and stress among others.
– The hypothalamus is connected to the pituitary gland to release hormones throughout the body.
– Basal Ganglion – located in front and to the side of the thalamus, this area is involved in regulating both cognitive thought patterns and motor movements. Problems with the basal ganglion can lead to obsessive‐compulsive disorder (not being able to turn off obsessive thoughts) and movement disorders such as Parkinson’s Disease or Huntington’ Disease
Brain Divisions: Forebrain
CingulateGyrus
9/11/2011
7
Forebrain: Limbic System– Limbic system is a collection of structures all related to emotion including the cingulate gyrus, hippocampus, and amygdala.
– Hippocampus – located inside the temporal lobe this structure is necessary to form long‐term episodic memories (but not as a storage area).
– Amygdala – located just in front of the hippocampus, this area assigns emotional value to stimuli and is involved in motivating our actions and can change based on our experience for example, in addiction the value of drugs or gambling changes in the amygdala to support continued use.
Cerebral Lobes
• Occipital Lobe ‐ center for vision ‐processing of visual sensory information
Cerebral Lobes
• Temporal Lobe ‐ center for hearing, memory, associations
Cerebral Lobes
• Parietal Lobe‐ center for sensory information
• Separated from the frontal lobe by the Central Sulcus
9/11/2011
8
Cerebral Lobes
• Frontal Lobe‐ center for planning, contains the motor cortex
Sensory & Motor Cortex
HPA axis – Stress SystemHypothalamus, Pituitary, Adrenal
Language System• Wernicke’s area = language comprehension• Broca’s area = language production
9/11/2011
9
Left / Right Lateralization of Functions
Note the difference in perceptions: Analytic / details Holistic
Evidence of LateralizationSplit Brain Patients
• Some types of epilepsy start in one area of the brain (focus) and spread to other areas.
• Today, 90% of epilepsy cases are treated with drug therapy.
• Surgery to remove the epileptic focus or cutting the corpus callosum is rarely used as a last resort.