Neural Communication Overview of CNS / PNS Electrical Signaling Chemical Signaling Central Nervous System Peripheral Nervous System Somatic = sensory & motor Autonomic = arousal state Parasympathetic = relaxation, not aroused Sympathetic = fight or flight response, stress Communication in the Nervous System 4 Common Components of a Neuron 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 Signals between 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 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 1
Overview of Electrical Signaling INPUT and PROCESSING Transmitter-gated receptor channels EPSP / IPSP produced by ion entry & exit Temporal & Spatial summation occurs in the soma TRANSMISSION and NT RELEASE Input Dendrites Synaptic Potentials Neurotransmitters open the ion channels to provide input Movement of positive or negative ions creates the electrical synaptic potential Input Dendrites Synaptic Potentials Depolarization = Na + enters increasing resting potential towards zero (less polarized) Hyperpolarization = K + exits decreases resting potential Missing from figure are the pumps that move Na + outside and K + inside using energy Processing / Decision making Soma Summation 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 2
Soma: Temporal & Spatial Summation Additional inputs that occur before the pumps return ions can add together Increased summation = the closer in space & time. Can occur through multiple inputs or a single neuron Temporal Spatial 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 Visualizing ionic transport during the action potential. +30 mv -70 mv +30-50 -70 1. Threshold opens voltage gated Na + channels = Rising Phase: Na + Entry 2. After Na + entry, voltage gated K + channels open = Falling Phase: K + Exit 0 1 2 3 4 msec 3. The Na+/K+ pump restores ion concentrations so next signal can be sent = Refractory Period: no action potentials Pumps working +30 +30-50 -75 +30 +30 3
Output Terminal Buttons Releasing Neurotransmitter Neurotransmitters stored in vesicles at terminal button Action potential at terminal releases neurotransmitter Neurotransmitter binds to receptors 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 neurotransmitters to act in different ways on the same target Eliminates interference or cross talk between close synapses 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 4
1 Brain Divisions: Hindbrain Neuroanatomy Slides Hindbrain, Midbrain, Forebrain Cortex Lobes Systems Pons Medulla Spinal Cord Cerebellum Hindbrain Brain Divisions: Midbrain 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. Superior Colliculus Inferior Colliculus 1 Tectum 5
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). Corpus Callosum Basal Ganglion Hypothalamus Pituitary Gland Brain Divisions: Forebrain Thalamus Forebrain Brain Divisions: 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. Cingulate Gyrus 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 obsessivecompulsive disorder (not being able to turn off obsessive thoughts) and movement disorders such as Parkinson s Disease or Huntington Disease 6
Forebrain: Limbic System Cerebral Lobes 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. Occipital Lobe center for vision processing of visual sensory information Cerebral Lobes Cerebral Lobes Temporal Lobe center for hearing, memory, associations Parietal Lobe center for sensory information Separated from the frontal lobe by the Central Sulcus 7
Cerebral Lobes Sensory & Motor Cortex Frontal Lobe center for planning, contains the motor cortex HPA axis Stress System Hypothalamus, Pituitary, Adrenal Language System Wernicke s area = language comprehension Broca s area = language production 8
Left / Right Lateralization of Functions Note the difference in perceptions: Analytic / details Holistic Evidence of Lateralization Split 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. 9